Provided by: systemd_253.5-1ubuntu6.1_amd64 bug

NAME

       systemd.network - Network configuration

SYNOPSIS

       network.network

DESCRIPTION

       A plain ini-style text file that encodes network configuration for matching network
       interfaces, used by systemd-networkd(8). See systemd.syntax(7) for a general description
       of the syntax.

       The main network file must have the extension .network; other extensions are ignored.
       Networks are applied to links whenever the links appear.

       The .network files are read from the files located in the system network directories
       /lib/systemd/network and /usr/local/lib/systemd/network, the volatile runtime network
       directory /run/systemd/network and the local administration network directory
       /etc/systemd/network. All configuration files are collectively sorted and processed in
       alphanumeric order, regardless of the directories in which they live. However, files with
       identical filenames replace each other. It is recommended that each filename is prefixed
       with a number (e.g.  10-eth0.network). Otherwise, the default .network files or those
       generated by systemd-network-generator.service(8) may take precedence over user configured
       files. Files in /etc/ have the highest priority, files in /run/ take precedence over files
       with the same name under /usr/. This can be used to override a system-supplied
       configuration file with a local file if needed. As a special case, an empty file (file
       size 0) or symlink with the same name pointing to /dev/null disables the configuration
       file entirely (it is "masked").

       Along with the network file foo.network, a "drop-in" directory foo.network.d/ may exist.
       All files with the suffix ".conf" from this directory will be merged in the alphanumeric
       order and parsed after the main file itself has been parsed. This is useful to alter or
       add configuration settings, without having to modify the main configuration file. Each
       drop-in file must have appropriate section headers.

       In addition to /etc/systemd/network, drop-in ".d" directories can be placed in
       /lib/systemd/network or /run/systemd/network directories. Drop-in files in /etc/ take
       precedence over those in /run/ which in turn take precedence over those in /lib/. Drop-in
       files under any of these directories take precedence over the main network file wherever
       located.

[MATCH] SECTION OPTIONS

       The network file contains a [Match] section, which determines if a given network file may
       be applied to a given interface; and a [Network] section specifying how the interface
       should be configured. The first (in alphanumeric order) of the network files that matches
       a given interface is applied, all later files are ignored, even if they match as well.

       A network file is said to match a network interface if all matches specified by the
       [Match] section are satisfied. When a network file does not contain valid settings in
       [Match] section, then the file will match all interfaces and systemd-networkd warns about
       that. Hint: to avoid the warning and to make it clear that all interfaces shall be
       matched, add the following:

           Name=*

       The following keys are accepted:

       MACAddress=
           A whitespace-separated list of hardware addresses. The acceptable formats are:

           colon-delimited hexadecimal
               Each field must be one byte. E.g.  "12:34:56:78:90:ab" or "AA:BB:CC:DD:EE:FF".

           hyphen-delimited hexadecimal
               Each field must be one byte. E.g.  "12-34-56-78-90-ab" or "AA-BB-CC-DD-EE-FF".

           dot-delimited hexadecimal
               Each field must be two bytes. E.g.  "1234.5678.90ab" or "AABB.CCDD.EEFF".

           IPv4 address format
               E.g.  "127.0.0.1" or "192.168.0.1".

           IPv6 address format
               E.g.  "2001:0db8:85a3::8a2e:0370:7334" or "::1".

           The total length of each MAC address must be 4 (for IPv4 tunnel), 6 (for Ethernet), 16
           (for IPv6 tunnel), or 20 (for InfiniBand). This option may appear more than once, in
           which case the lists are merged. If the empty string is assigned to this option, the
           list of hardware addresses defined prior to this is reset. Defaults to unset.

       PermanentMACAddress=
           A whitespace-separated list of hardware's permanent addresses. While MACAddress=
           matches the device's current MAC address, this matches the device's permanent MAC
           address, which may be different from the current one. Use full colon-, hyphen- or
           dot-delimited hexadecimal, or IPv4 or IPv6 address format. This option may appear more
           than once, in which case the lists are merged. If the empty string is assigned to this
           option, the list of hardware addresses defined prior to this is reset. Defaults to
           unset.

       Path=
           A whitespace-separated list of shell-style globs matching the persistent path, as
           exposed by the udev property ID_PATH.

       Driver=
           A whitespace-separated list of shell-style globs matching the driver currently bound
           to the device, as exposed by the udev property ID_NET_DRIVER of its parent device, or
           if that is not set, the driver as exposed by ethtool -i of the device itself. If the
           list is prefixed with a "!", the test is inverted.

       Type=
           A whitespace-separated list of shell-style globs matching the device type, as exposed
           by networkctl list. If the list is prefixed with a "!", the test is inverted. Some
           valid values are "ether", "loopback", "wlan", "wwan". Valid types are named either
           from the udev "DEVTYPE" attribute, or "ARPHRD_" macros in linux/if_arp.h, so this is
           not comprehensive.

       Kind=
           A whitespace-separated list of shell-style globs matching the device kind, as exposed
           by networkctl status INTERFACE or ip -d link show INTERFACE. If the list is prefixed
           with a "!", the test is inverted. Some valid values are "bond", "bridge", "gre",
           "tun", "veth". Valid kinds are given by netlink's "IFLA_INFO_KIND" attribute, so this
           is not comprehensive.

       Property=
           A whitespace-separated list of udev property names with their values after equals sign
           ("="). If multiple properties are specified, the test results are ANDed. If the list
           is prefixed with a "!", the test is inverted. If a value contains white spaces, then
           please quote whole key and value pair. If a value contains quotation, then please
           escape the quotation with "\".

           Example: if a .link file has the following:

               Property=ID_MODEL_ID=9999 "ID_VENDOR_FROM_DATABASE=vendor name" "KEY=with \"quotation\""

           then, the .link file matches only when an interface has all the above three
           properties.

       Name=
           A whitespace-separated list of shell-style globs matching the device name, as exposed
           by the udev property "INTERFACE", or device's alternative names. If the list is
           prefixed with a "!", the test is inverted.

       WLANInterfaceType=
           A whitespace-separated list of wireless network type. Supported values are "ad-hoc",
           "station", "ap", "ap-vlan", "wds", "monitor", "mesh-point", "p2p-client", "p2p-go",
           "p2p-device", "ocb", and "nan". If the list is prefixed with a "!", the test is
           inverted.

       SSID=
           A whitespace-separated list of shell-style globs matching the SSID of the currently
           connected wireless LAN. If the list is prefixed with a "!", the test is inverted.

       BSSID=
           A whitespace-separated list of hardware address of the currently connected wireless
           LAN. Use full colon-, hyphen- or dot-delimited hexadecimal. See the example in
           MACAddress=. This option may appear more than once, in which case the lists are
           merged. If the empty string is assigned to this option, the list is reset.

       Host=
           Matches against the hostname or machine ID of the host. See ConditionHost= in
           systemd.unit(5) for details. When prefixed with an exclamation mark ("!"), the result
           is negated. If an empty string is assigned, the previously assigned value is cleared.

       Virtualization=
           Checks whether the system is executed in a virtualized environment and optionally test
           whether it is a specific implementation. See ConditionVirtualization= in
           systemd.unit(5) for details. When prefixed with an exclamation mark ("!"), the result
           is negated. If an empty string is assigned, the previously assigned value is cleared.

       KernelCommandLine=
           Checks whether a specific kernel command line option is set. See
           ConditionKernelCommandLine= in systemd.unit(5) for details. When prefixed with an
           exclamation mark ("!"), the result is negated. If an empty string is assigned, the
           previously assigned value is cleared.

       KernelVersion=
           Checks whether the kernel version (as reported by uname -r) matches a certain
           expression. See ConditionKernelVersion= in systemd.unit(5) for details. When prefixed
           with an exclamation mark ("!"), the result is negated. If an empty string is assigned,
           the previously assigned value is cleared.

       Credential=
           Checks whether the specified credential was passed to the systemd-udevd.service
           service. See System and Service Credentials[1] for details. When prefixed with an
           exclamation mark ("!"), the result is negated. If an empty string is assigned, the
           previously assigned value is cleared.

       Architecture=
           Checks whether the system is running on a specific architecture. See
           ConditionArchitecture= in systemd.unit(5) for details. When prefixed with an
           exclamation mark ("!"), the result is negated. If an empty string is assigned, the
           previously assigned value is cleared.

       Firmware=
           Checks whether the system is running on a machine with the specified firmware. See
           ConditionFirmware= in systemd.unit(5) for details. When prefixed with an exclamation
           mark ("!"), the result is negated. If an empty string is assigned, the previously
           assigned value is cleared.

[LINK] SECTION OPTIONS

       The [Link] section accepts the following keys:

       MACAddress=
           The hardware address to set for the device.

       MTUBytes=
           The maximum transmission unit in bytes to set for the device. The usual suffixes K, M,
           G, are supported and are understood to the base of 1024.

           Note that if IPv6 is enabled on the interface, and the MTU is chosen below 1280 (the
           minimum MTU for IPv6) it will automatically be increased to this value.

       ARP=
           Takes a boolean. If set to true, the ARP (low-level Address Resolution Protocol) for
           this interface is enabled. When unset, the kernel's default will be used.

           For example, disabling ARP is useful when creating multiple MACVLAN or VLAN virtual
           interfaces atop a single lower-level physical interface, which will then only serve as
           a link/"bridge" device aggregating traffic to the same physical link and not
           participate in the network otherwise. Defaults to unset.

       Multicast=
           Takes a boolean. If set to true, the multicast flag on the device is enabled. Defaults
           to unset.

       AllMulticast=
           Takes a boolean. If set to true, the driver retrieves all multicast packets from the
           network. This happens when multicast routing is enabled. Defaults to unset.

       Promiscuous=
           Takes a boolean. If set to true, promiscuous mode of the interface is enabled.
           Defaults to unset.

           If this is set to false for the underlying link of a "passthru" mode MACVLAN/MACVTAP,
           the virtual interface will be created with the "nopromisc" flag set.

       Unmanaged=
           Takes a boolean. When "yes", no attempts are made to bring up or configure matching
           links, equivalent to when there are no matching network files. Defaults to "no".

           This is useful for preventing later matching network files from interfering with
           certain interfaces that are fully controlled by other applications.

       Group=
           Link groups are similar to port ranges found in managed switches. When network
           interfaces are added to a numbered group, operations on all the interfaces from that
           group can be performed at once. Takes an unsigned integer in the range 0...2147483647.
           Defaults to unset.

       RequiredForOnline=
           Takes a boolean or a minimum operational state and an optional maximum operational
           state. Please see networkctl(1) for possible operational states. When "yes", the
           network is deemed required when determining whether the system is online (including
           when running systemd-networkd-wait-online). When "no", the network is ignored when
           determining the online state. When a minimum operational state and an optional maximum
           operational state are set, "yes" is implied, and this controls the minimum and maximum
           operational state required for the network interface to be considered online.

           Defaults to "yes" when ActivationPolicy= is not set, or set to "up", "always-up", or
           "bound". Defaults to "no" when ActivationPolicy= is set to "manual" or "down". This is
           forced to "no" when ActivationPolicy= is set to "always-down".

           The network will be brought up normally (as configured by ActivationPolicy=), but in
           the event that there is no address being assigned by DHCP or the cable is not plugged
           in, the link will simply remain offline and be skipped automatically by
           systemd-networkd-wait-online if "RequiredForOnline=no".

       RequiredFamilyForOnline=
           Takes an address family. When specified, an IP address in the given family is deemed
           required when determining whether the link is online (including when running
           systemd-networkd-wait-online). Takes one of "ipv4", "ipv6", "both", or "any". Defaults
           to "any". Note that this option has no effect if "RequiredForOnline=no", or if
           "RequiredForOnline=" specifies a minimum operational state below "degraded".

       ActivationPolicy=
           Specifies the policy for systemd-networkd managing the link administrative state.
           Specifically, this controls how systemd-networkd changes the network device's "IFF_UP"
           flag, which is sometimes controlled by system administrators by running e.g., ip link
           set dev eth0 up or ip link set dev eth0 down, and can also be changed with networkctl
           up eth0 or networkctl down eth0.

           Takes one of "up", "always-up", "manual", "always-down", "down", or "bound". When
           "manual", systemd-networkd will not change the link's admin state automatically; the
           system administrator must bring the interface up or down manually, as desired. When
           "up" (the default) or "always-up", or "down" or "always-down", systemd-networkd will
           set the link up or down, respectively, when the interface is (re)configured. When
           "always-up" or "always-down", systemd-networkd will set the link up or down,
           respectively, any time systemd-networkd detects a change in the administrative state.
           When BindCarrier= is also set, this is automatically set to "bound" and any other
           value is ignored.

           When the policy is set to "down" or "manual", the default value of RequiredForOnline=
           is "no". When the policy is set to "always-down", the value of RequiredForOnline=
           forced to "no".

           The administrative state is not the same as the carrier state, so using "always-up"
           does not mean the link will never lose carrier. The link carrier depends on both the
           administrative state as well as the network device's physical connection. However, to
           avoid reconfiguration failures, when using "always-up", IgnoreCarrierLoss= is forced
           to true.

[SR-IOV] SECTION OPTIONS

       The [SR-IOV] section accepts the following keys. Specify several [SR-IOV] sections to
       configure several SR-IOVs. SR-IOV provides the ability to partition a single physical PCI
       resource into virtual PCI functions which can then be injected into a VM. In the case of
       network VFs, SR-IOV improves north-south network performance (that is, traffic with
       endpoints outside the host machine) by allowing traffic to bypass the host machine’s
       network stack.

       VirtualFunction=
           Specifies a Virtual Function (VF), lightweight PCIe function designed solely to move
           data in and out. Takes an integer in the range 0...2147483646. This option is
           compulsory.

       VLANId=
           Specifies VLAN ID of the virtual function. Takes an integer in the range 1...4095.

       QualityOfService=
           Specifies quality of service of the virtual function. Takes an integer in the range
           1...4294967294.

       VLANProtocol=
           Specifies VLAN protocol of the virtual function. Takes "802.1Q" or "802.1ad".

       MACSpoofCheck=
           Takes a boolean. Controls the MAC spoof checking. When unset, the kernel's default
           will be used.

       QueryReceiveSideScaling=
           Takes a boolean. Toggle the ability of querying the receive side scaling (RSS)
           configuration of the virtual function (VF). The VF RSS information like RSS hash key
           may be considered sensitive on some devices where this information is shared between
           VF and the physical function (PF). When unset, the kernel's default will be used.

       Trust=
           Takes a boolean. Allows one to set trust mode of the virtual function (VF). When set,
           VF users can set a specific feature which may impact security and/or performance. When
           unset, the kernel's default will be used.

       LinkState=
           Allows one to set the link state of the virtual function (VF). Takes a boolean or a
           special value "auto". Setting to "auto" means a reflection of the physical function
           (PF) link state, "yes" lets the VF to communicate with other VFs on this host even if
           the PF link state is down, "no" causes the hardware to drop any packets sent by the
           VF. When unset, the kernel's default will be used.

       MACAddress=
           Specifies the MAC address for the virtual function.

[NETWORK] SECTION OPTIONS

       The [Network] section accepts the following keys:

       Description=
           A description of the device. This is only used for presentation purposes.

       DHCP=
           Enables DHCPv4 and/or DHCPv6 client support. Accepts "yes", "no", "ipv4", or "ipv6".
           Defaults to "no".

           Note that DHCPv6 will by default be triggered by Router Advertisements, if reception
           is enabled, regardless of this parameter. By explicitly enabling DHCPv6 support here,
           the DHCPv6 client will be started in the mode specified by the WithoutRA= setting in
           the [DHCPv6] section, regardless of the presence of routers on the link, or what flags
           the routers pass. See IPv6AcceptRA=.

           Furthermore, note that by default the domain name specified through DHCP, on Ubuntu,
           are used for name resolution. See option UseDomains= below.

           See the [DHCPv4] or [DHCPv6] sections below for further configuration options for the
           DHCP client support.

       DHCPServer=
           Takes a boolean. If set to "yes", DHCPv4 server will be started. Defaults to "no".
           Further settings for the DHCP server may be set in the [DHCPServer] section described
           below.

       LinkLocalAddressing=
           Enables link-local address autoconfiguration. Accepts yes, no, ipv4, and ipv6. An IPv6
           link-local address is configured when yes or ipv6. An IPv4 link-local address is
           configured when yes or ipv4 and when DHCPv4 autoconfiguration has been unsuccessful
           for some time. (IPv4 link-local address autoconfiguration will usually happen in
           parallel with repeated attempts to acquire a DHCPv4 lease).

           Defaults to no when KeepMaster= or Bridge= is set or when the specified
           MACVLAN=/MACVTAP= has Mode=passthru, or ipv6 otherwise.

       IPv6LinkLocalAddressGenerationMode=
           Specifies how IPv6 link-local address is generated. Takes one of "eui64", "none",
           "stable-privacy" and "random". When unset, "stable-privacy" is used if
           IPv6StableSecretAddress= is specified, and if not, "eui64" is used. Note that if
           LinkLocalAddressing= is "no" or "ipv4", then IPv6LinkLocalAddressGenerationMode= will
           be ignored. Also, even if LinkLocalAddressing= is "yes" or "ipv6", setting
           IPv6LinkLocalAddressGenerationMode=none disables to configure an IPv6 link-local
           address.

       IPv6StableSecretAddress=
           Takes an IPv6 address. The specified address will be used as a stable secret for
           generating IPv6 link-local address. If this setting is specified, and
           IPv6LinkLocalAddressGenerationMode= is unset, then
           IPv6LinkLocalAddressGenerationMode=stable-privacy is implied. If this setting is not
           specified, and "stable-privacy" is set to IPv6LinkLocalAddressGenerationMode=, then a
           stable secret address will be generated from the local machine ID and the interface
           name.

       IPv4LLStartAddress=
           Specifies the first IPv4 link-local address to try. Takes an IPv4 address for example
           169.254.1.2, from the link-local address range: 169.254.0.0/16 except for
           169.254.0.0/24 and 169.254.255.0/24. This setting may be useful if the device should
           always have the same address as long as there is no address conflict. When unset, a
           random address will be automatically selected. Defaults to unset.

       IPv4LLRoute=
           Takes a boolean. If set to true, sets up the route needed for non-IPv4LL hosts to
           communicate with IPv4LL-only hosts. Defaults to false.

       DefaultRouteOnDevice=
           Takes a boolean. If set to true, sets up the IPv4 default route bound to the
           interface. Defaults to false. This is useful when creating routes on point-to-point
           interfaces. This is equivalent to e.g. the following,

               ip route add default dev veth99

           or,

               [Route]
               Gateway=0.0.0.0

           Currently, there are no way to specify e.g., the table for the route configured by
           this setting. To configure the default route with such an additional property, please
           use the following instead:

               [Route]
               Gateway=0.0.0.0
               Table=1234

           If you'd like to create an IPv6 default route bound to the interface, please use the
           following:

               [Route]
               Gateway=::
               Table=1234

       LLMNR=
           Takes a boolean or "resolve". When true, enables Link-Local Multicast Name
           Resolution[2] on the link. When set to "resolve", only resolution is enabled, but not
           host registration and announcement. Defaults to true. This setting is read by systemd-
           resolved.service(8).

       MulticastDNS=
           Takes a boolean or "resolve". When true, enables Multicast DNS[3] support on the link.
           When set to "resolve", only resolution is enabled, but not host or service
           registration and announcement. Defaults to false. This setting is read by systemd-
           resolved.service(8).

       DNSOverTLS=
           Takes a boolean or "opportunistic". When true, enables DNS-over-TLS[4] support on the
           link. When set to "opportunistic", compatibility with non-DNS-over-TLS servers is
           increased, by automatically turning off DNS-over-TLS servers in this case. This option
           defines a per-interface setting for resolved.conf(5)'s global DNSOverTLS= option.
           Defaults to unset, and the global setting will be used. This setting is read by
           systemd-resolved.service(8).

       DNSSEC=
           Takes a boolean or "allow-downgrade". When true, enables DNSSEC[5] DNS validation
           support on the link. When set to "allow-downgrade", compatibility with non-DNSSEC
           capable networks is increased, by automatically turning off DNSSEC in this case. This
           option defines a per-interface setting for resolved.conf(5)'s global DNSSEC= option.
           Defaults to unset, and the global setting will be used. This setting is read by
           systemd-resolved.service(8).

       DNSSECNegativeTrustAnchors=
           A space-separated list of DNSSEC negative trust anchor domains. If specified and
           DNSSEC is enabled, look-ups done via the interface's DNS server will be subject to the
           list of negative trust anchors, and not require authentication for the specified
           domains, or anything below it. Use this to disable DNSSEC authentication for specific
           private domains, that cannot be proven valid using the Internet DNS hierarchy.
           Defaults to the empty list. This setting is read by systemd-resolved.service(8).

       LLDP=
           Controls support for Ethernet LLDP packet reception. LLDP is a link-layer protocol
           commonly implemented on professional routers and bridges which announces which
           physical port a system is connected to, as well as other related data. Accepts a
           boolean or the special value "routers-only". When true, incoming LLDP packets are
           accepted and a database of all LLDP neighbors maintained. If "routers-only" is set
           only LLDP data of various types of routers is collected and LLDP data about other
           types of devices ignored (such as stations, telephones and others). If false, LLDP
           reception is disabled. Defaults to "routers-only". Use networkctl(1) to query the
           collected neighbor data. LLDP is only available on Ethernet links. See EmitLLDP= below
           for enabling LLDP packet emission from the local system.

       EmitLLDP=
           Controls support for Ethernet LLDP packet emission. Accepts a boolean parameter or the
           special values "nearest-bridge", "non-tpmr-bridge" and "customer-bridge". Defaults to
           false, which turns off LLDP packet emission. If not false, a short LLDP packet with
           information about the local system is sent out in regular intervals on the link. The
           LLDP packet will contain information about the local hostname, the local machine ID
           (as stored in machine-id(5)) and the local interface name, as well as the pretty
           hostname of the system (as set in machine-info(5)). LLDP emission is only available on
           Ethernet links. Note that this setting passes data suitable for identification of host
           to the network and should thus not be enabled on untrusted networks, where such
           identification data should not be made available. Use this option to permit other
           systems to identify on which interfaces they are connected to this system. The three
           special values control propagation of the LLDP packets. The "nearest-bridge" setting
           permits propagation only to the nearest connected bridge, "non-tpmr-bridge" permits
           propagation across Two-Port MAC Relays, but not any other bridges, and
           "customer-bridge" permits propagation until a customer bridge is reached. For details
           about these concepts, see IEEE 802.1AB-2016[6]. Note that configuring this setting to
           true is equivalent to "nearest-bridge", the recommended and most restricted level of
           propagation. See LLDP= above for an option to enable LLDP reception.

       BindCarrier=
           A link name or a list of link names. When set, controls the behavior of the current
           link. When all links in the list are in an operational down state, the current link is
           brought down. When at least one link has carrier, the current interface is brought up.

           This forces ActivationPolicy= to be set to "bound".

       Address=
           A static IPv4 or IPv6 address and its prefix length, separated by a "/" character.
           Specify this key more than once to configure several addresses. The format of the
           address must be as described in inet_pton(3). This is a short-hand for an [Address]
           section only containing an Address key (see below). This option may be specified more
           than once.

           If the specified address is "0.0.0.0" (for IPv4) or "::" (for IPv6), a new address
           range of the requested size is automatically allocated from a system-wide pool of
           unused ranges. Note that the prefix length must be equal or larger than 8 for IPv4,
           and 64 for IPv6. The allocated range is checked against all current network interfaces
           and all known network configuration files to avoid address range conflicts. The
           default system-wide pool consists of 192.168.0.0/16, 172.16.0.0/12 and 10.0.0.0/8 for
           IPv4, and fd00::/8 for IPv6. This functionality is useful to manage a large number of
           dynamically created network interfaces with the same network configuration and
           automatic address range assignment.

       Gateway=
           The gateway address, which must be in the format described in inet_pton(3). This is a
           short-hand for a [Route] section only containing a Gateway= key. This option may be
           specified more than once.

       DNS=
           A DNS server address, which must be in the format described in inet_pton(3). This
           option may be specified more than once. Each address can optionally take a port number
           separated with ":", a network interface name or index separated with "%", and a Server
           Name Indication (SNI) separated with "#". When IPv6 address is specified with a port
           number, then the address must be in the square brackets. That is, the acceptable full
           formats are "111.222.333.444:9953%ifname#example.com" for IPv4 and
           "[1111:2222::3333]:9953%ifname#example.com" for IPv6. If an empty string is assigned,
           then the all previous assignments are cleared. This setting is read by systemd-
           resolved.service(8).

       Domains=
           A whitespace-separated list of domains which should be resolved using the DNS servers
           on this link. Each item in the list should be a domain name, optionally prefixed with
           a tilde ("~"). The domains with the prefix are called "routing-only domains". The
           domains without the prefix are called "search domains" and are first used as search
           suffixes for extending single-label hostnames (hostnames containing no dots) to become
           fully qualified domain names (FQDNs). If a single-label hostname is resolved on this
           interface, each of the specified search domains are appended to it in turn, converting
           it into a fully qualified domain name, until one of them may be successfully resolved.

           Both "search" and "routing-only" domains are used for routing of DNS queries: look-ups
           for hostnames ending in those domains (hence also single label names, if any "search
           domains" are listed), are routed to the DNS servers configured for this interface. The
           domain routing logic is particularly useful on multi-homed hosts with DNS servers
           serving particular private DNS zones on each interface.

           The "routing-only" domain "~."  (the tilde indicating definition of a routing domain,
           the dot referring to the DNS root domain which is the implied suffix of all valid DNS
           names) has special effect. It causes all DNS traffic which does not match another
           configured domain routing entry to be routed to DNS servers specified for this
           interface. This setting is useful to prefer a certain set of DNS servers if a link on
           which they are connected is available.

           This setting is read by systemd-resolved.service(8). "Search domains" correspond to
           the domain and search entries in resolv.conf(5). Domain name routing has no equivalent
           in the traditional glibc API, which has no concept of domain name servers limited to a
           specific link.

       DNSDefaultRoute=
           Takes a boolean argument. If true, this link's configured DNS servers are used for
           resolving domain names that do not match any link's configured Domains= setting. If
           false, this link's configured DNS servers are never used for such domains, and are
           exclusively used for resolving names that match at least one of the domains configured
           on this link. If not specified defaults to an automatic mode: queries not matching any
           link's configured domains will be routed to this link if it has no routing-only
           domains configured.

       NTP=
           An NTP server address (either an IP address, or a hostname). This option may be
           specified more than once. This setting is read by systemd-timesyncd.service(8).

       IPForward=
           Configures IP packet forwarding for the system. If enabled, incoming packets on any
           network interface will be forwarded to any other interfaces according to the routing
           table. Takes a boolean, or the values "ipv4" or "ipv6", which only enable IP packet
           forwarding for the specified address family. This controls the net.ipv4.ip_forward and
           net.ipv6.conf.all.forwarding sysctl options of the network interface (see IP Sysctl[7]
           for details about sysctl options). Defaults to "no".

           Note: this setting controls a global kernel option, and does so one way only: if a
           network that has this setting enabled is set up the global setting is turned on.
           However, it is never turned off again, even after all networks with this setting
           enabled are shut down again.

           To allow IP packet forwarding only between specific network interfaces use a firewall.

       IPMasquerade=
           Configures IP masquerading for the network interface. If enabled, packets forwarded
           from the network interface will be appear as coming from the local host. Takes one of
           "ipv4", "ipv6", "both", or "no". Defaults to "no". If enabled, this automatically sets
           IPForward= to one of "ipv4", "ipv6" or "yes".

           Note. Any positive boolean values such as "yes" or "true" are now deprecated. Please
           use one of the values in the above.

       IPv6PrivacyExtensions=
           Configures use of stateless temporary addresses that change over time (see RFC
           4941[8], Privacy Extensions for Stateless Address Autoconfiguration in IPv6). Takes a
           boolean or the special values "prefer-public" and "kernel". When true, enables the
           privacy extensions and prefers temporary addresses over public addresses. When
           "prefer-public", enables the privacy extensions, but prefers public addresses over
           temporary addresses. When false, the privacy extensions remain disabled. When
           "kernel", the kernel's default setting will be left in place. Defaults to "no".

       IPv6AcceptRA=
           Takes a boolean. Controls IPv6 Router Advertisement (RA) reception support for the
           interface. If true, RAs are accepted; if false, RAs are ignored. When RAs are
           accepted, they may trigger the start of the DHCPv6 client if the relevant flags are
           set in the RA data, or if no routers are found on the link. The default is to disable
           RA reception for bridge devices or when IP forwarding is enabled, and to enable it
           otherwise. Cannot be enabled on devices aggregated in a bond device or when link-local
           addressing is disabled.

           Further settings for the IPv6 RA support may be configured in the [IPv6AcceptRA]
           section, see below.

           Also see IP Sysctl[7] in the kernel documentation regarding "accept_ra", but note that
           systemd's setting of 1 (i.e. true) corresponds to kernel's setting of 2.

           Note that kernel's implementation of the IPv6 RA protocol is always disabled,
           regardless of this setting. If this option is enabled, a userspace implementation of
           the IPv6 RA protocol is used, and the kernel's own implementation remains disabled,
           since systemd-networkd needs to know all details supplied in the advertisements, and
           these are not available from the kernel if the kernel's own implementation is used.

       IPv6DuplicateAddressDetection=
           Configures the amount of IPv6 Duplicate Address Detection (DAD) probes to send. When
           unset, the kernel's default will be used.

       IPv6HopLimit=
           Configures IPv6 Hop Limit. For each router that forwards the packet, the hop limit is
           decremented by 1. When the hop limit field reaches zero, the packet is discarded. When
           unset, the kernel's default will be used.

       IPv4AcceptLocal=
           Takes a boolean. Accept packets with local source addresses. In combination with
           suitable routing, this can be used to direct packets between two local interfaces over
           the wire and have them accepted properly. When unset, the kernel's default will be
           used.

       IPv4RouteLocalnet=
           Takes a boolean. When true, the kernel does not consider loopback addresses as martian
           source or destination while routing. This enables the use of 127.0.0.0/8 for local
           routing purposes. When unset, the kernel's default will be used.

       IPv4ProxyARP=
           Takes a boolean. Configures proxy ARP for IPv4. Proxy ARP is the technique in which
           one host, usually a router, answers ARP requests intended for another machine. By
           "faking" its identity, the router accepts responsibility for routing packets to the
           "real" destination. See RFC 1027[9]. When unset, the kernel's default will be used.

       IPv6ProxyNDP=
           Takes a boolean. Configures proxy NDP for IPv6. Proxy NDP (Neighbor Discovery
           Protocol) is a technique for IPv6 to allow routing of addresses to a different
           destination when peers expect them to be present on a certain physical link. In this
           case a router answers Neighbour Advertisement messages intended for another machine by
           offering its own MAC address as destination. Unlike proxy ARP for IPv4, it is not
           enabled globally, but will only send Neighbour Advertisement messages for addresses in
           the IPv6 neighbor proxy table, which can also be shown by ip -6 neighbour show proxy.
           systemd-networkd will control the per-interface `proxy_ndp` switch for each configured
           interface depending on this option. When unset, the kernel's default will be used.

       IPv6ProxyNDPAddress=
           An IPv6 address, for which Neighbour Advertisement messages will be proxied. This
           option may be specified more than once. systemd-networkd will add the
           IPv6ProxyNDPAddress= entries to the kernel's IPv6 neighbor proxy table. This setting
           implies IPv6ProxyNDP=yes but has no effect if IPv6ProxyNDP= has been set to false.
           When unset, the kernel's default will be used.

       IPv6SendRA=
           Whether to enable or disable Router Advertisement sending on a link. Takes a boolean
           value. When enabled, prefixes configured in [IPv6Prefix] sections and routes
           configured in the [IPv6RoutePrefix] sections are distributed as defined in the
           [IPv6SendRA] section. If DHCPPrefixDelegation= is enabled, then the delegated prefixes
           are also distributed. See DCHPPrefixDelegation= setting and the [IPv6SendRA],
           [IPv6Prefix], [IPv6RoutePrefix], and [DHCPPrefixDelegation] sections for more
           configuration options.

       DHCPPrefixDelegation=
           Takes a boolean value. When enabled, requests subnet prefixes on another link via the
           DHCPv6 protocol or via the 6RD option in the DHCPv4 protocol. An address within each
           delegated prefix will be assigned, and the prefixes will be announced through IPv6
           Router Advertisement if IPv6SendRA= is enabled. This behaviour can be configured in
           the [DHCPPrefixDelegation] section. Defaults to disabled.

       IPv6MTUBytes=
           Configures IPv6 maximum transmission unit (MTU). An integer greater than or equal to
           1280 bytes. When unset, the kernel's default will be used.

       KeepMaster=
           Takes a boolean value. When enabled, the current master interface index will not be
           changed, and BatmanAdvanced=, Bond=, Bridge=, and VRF= settings are ignored. This may
           be useful when a netdev with a master interface is created by another program, e.g.
           systemd-nspawn(1). Defaults to false.

       BatmanAdvanced=, Bond=, Bridge=, VRF=
           The name of the B.A.T.M.A.N. Advanced, bond, bridge, or VRF interface to add the link
           to. See systemd.netdev(5).

       IPoIB=, IPVLAN=, IPVTAP=, MACsec=, MACVLAN=, MACVTAP=, Tunnel=, VLAN=, VXLAN=, Xfrm=
           The name of an IPoIB, IPVLAN, IPVTAP, MACsec, MACVLAN, MACVTAP, tunnel, VLAN, VXLAN,
           or Xfrm to be created on the link. See systemd.netdev(5). This option may be specified
           more than once.

       ActiveSlave=
           Takes a boolean. Specifies the new active slave. The "ActiveSlave=" option is only
           valid for following modes: "active-backup", "balance-alb", and "balance-tlb". Defaults
           to false.

       PrimarySlave=
           Takes a boolean. Specifies which slave is the primary device. The specified device
           will always be the active slave while it is available. Only when the primary is
           off-line will alternate devices be used. This is useful when one slave is preferred
           over another, e.g. when one slave has higher throughput than another. The
           "PrimarySlave=" option is only valid for following modes: "active-backup",
           "balance-alb", and "balance-tlb". Defaults to false.

       ConfigureWithoutCarrier=
           Takes a boolean. Allows networkd to configure a specific link even if it has no
           carrier. Defaults to false. If enabled, and the IgnoreCarrierLoss= setting is not
           explicitly set, then it is enabled as well.

       IgnoreCarrierLoss=
           Takes a boolean or a timespan. When true, systemd-networkd retains both the static and
           dynamic configuration of the interface even if its carrier is lost. When false,
           systemd-networkd drops both the static and dynamic configuration of the interface.
           When a timespan is specified, systemd-networkd waits for the specified timespan, and
           ignores the carrier loss if the link regain its carrier within the timespan. Setting 0
           seconds is equivalent to "no", and "infinite" is equivalent to "yes".

           Setting a finite timespan may be useful when e.g. in the following cases:

           •   A wireless interface connecting to a network which has multiple access points with
               the same SSID.

           •   Enslaving a wireless interface to a bond interface, which may disconnect from the
               connected access point and causes its carrier to be lost.

           •   The driver of the interface resets when the MTU is changed.

           When Bond= is specified to a wireless interface, defaults to 3 seconds. When the
           DHCPv4 client is enabled and UseMTU= in the [DHCPv4] section enabled, defaults to 5
           seconds. Otherwise, defaults to the value specified with ConfigureWithoutCarrier=.
           When ActivationPolicy= is set to "always-up", this is forced to "yes", and ignored any
           user specified values.

       KeepConfiguration=
           Takes a boolean or one of "static", "dhcp-on-stop", "dhcp". When "static",
           systemd-networkd will not drop static addresses and routes on starting up process.
           When set to "dhcp-on-stop", systemd-networkd will not drop addresses and routes on
           stopping the daemon. When "dhcp", the addresses and routes provided by a DHCP server
           will never be dropped even if the DHCP lease expires. This is contrary to the DHCP
           specification, but may be the best choice if, e.g., the root filesystem relies on this
           connection. The setting "dhcp" implies "dhcp-on-stop", and "yes" implies "dhcp" and
           "static". Defaults to "dhcp-on-stop" when systemd-networkd is running in initrd, "yes"
           when the root filesystem is a network filesystem, and "no" otherwise.

[ADDRESS] SECTION OPTIONS

       An [Address] section accepts the following keys. Specify several [Address] sections to
       configure several addresses.

       Address=
           As in the [Network] section. This setting is mandatory. Each [Address] section can
           contain one Address= setting.

       Peer=
           The peer address in a point-to-point connection. Accepts the same format as the
           Address= setting.

       Broadcast=
           Takes an IPv4 address or boolean value. The address must be in the format described in
           inet_pton(3). If set to true, then the IPv4 broadcast address will be derived from the
           Address= setting. If set to false, then the broadcast address will not be set.
           Defaults to true, except for wireguard interfaces, where it default to false.

       Label=
           Specifies the label for the IPv4 address. The label must be a 7-bit ASCII string with
           a length of 1...15 characters. Defaults to unset.

       PreferredLifetime=
           Allows the default "preferred lifetime" of the address to be overridden. Only three
           settings are accepted: "forever", "infinity", which is the default and means that the
           address never expires, and "0", which means that the address is considered immediately
           "expired" and will not be used, unless explicitly requested. A setting of
           PreferredLifetime=0 is useful for addresses which are added to be used only by a
           specific application, which is then configured to use them explicitly.

       Scope=
           The scope of the address, which can be "global" (valid everywhere on the network, even
           through a gateway), "link" (only valid on this device, will not traverse a gateway) or
           "host" (only valid within the device itself, e.g. 127.0.0.1) or an integer in the
           range 0...255. Defaults to "global".

       RouteMetric=
           The metric of the prefix route, which is pointing to the subnet of the configured IP
           address, taking the configured prefix length into account. Takes an unsigned integer
           in the range 0...4294967295. When unset or set to 0, the kernel's default value is
           used. This setting will be ignored when AddPrefixRoute= is false.

       HomeAddress=
           Takes a boolean. Designates this address the "home address" as defined in RFC
           6275[10]. Supported only on IPv6. Defaults to false.

       DuplicateAddressDetection=
           Takes one of "ipv4", "ipv6", "both", or "none". When "ipv4", performs IPv4 Address
           Conflict Detection. See RFC 5227[11]. When "ipv6", performs IPv6 Duplicate Address
           Detection. See RFC 4862[12]. Defaults to "ipv4" for IPv4 link-local addresses, "ipv6"
           for IPv6 addresses, and "none" otherwise.

       ManageTemporaryAddress=
           Takes a boolean. If true the kernel manage temporary addresses created from this one
           as template on behalf of Privacy Extensions RFC 3041[13]. For this to become active,
           the use_tempaddr sysctl setting has to be set to a value greater than zero. The given
           address needs to have a prefix length of 64. This flag allows using privacy extensions
           in a manually configured network, just like if stateless auto-configuration was
           active. Defaults to false.

       AddPrefixRoute=
           Takes a boolean. When true, the prefix route for the address is automatically added.
           Defaults to true.

       AutoJoin=
           Takes a boolean. Joining multicast group on ethernet level via ip maddr command would
           not work if we have an Ethernet switch that does IGMP snooping since the switch would
           not replicate multicast packets on ports that did not have IGMP reports for the
           multicast addresses. Linux vxlan interfaces created via ip link add vxlan or
           networkd's netdev kind vxlan have the group option that enables them to do the
           required join. By extending ip address command with option "autojoin" we can get
           similar functionality for openvswitch (OVS) vxlan interfaces as well as other
           tunneling mechanisms that need to receive multicast traffic. Defaults to "no".

       NetLabel=label
           This setting provides a method for integrating static and dynamic network
           configuration into Linux NetLabel[14] subsystem rules, used by Linux Security Modules
           (LSMs)[15] for network access control. The label, with suitable LSM rules, can be used
           to control connectivity of (for example) a service with peers in the local network. At
           least with SELinux, only the ingress can be controlled but not egress. The benefit of
           using this setting is that it may be possible to apply interface independent part of
           NetLabel configuration at very early stage of system boot sequence, at the time when
           the network interfaces are not available yet, with netlabelctl(8), and the
           per-interface configuration with systemd-networkd once the interfaces appear later.
           Currently this feature is only implemented for SELinux.

           The option expects a single NetLabel label. The label must conform to lexical
           restrictions of LSM labels. When an interface is configured with IP addresses, the
           addresses and subnetwork masks will be appended to the NetLabel Fallback Peer
           Labeling[16] rules. They will be removed when the interface is deconfigured. Failures
           to manage the labels will be ignored.

           Warning: Once labeling is enabled for network traffic, a lot of LSM access control
           points in Linux networking stack go from dormant to active. Care should be taken to
           avoid getting into a situation where for example remote connectivity is broken, when
           the security policy hasn't been updated to consider LSM per-packet access controls and
           no rules would allow any network traffic. Also note that additional configuration with
           netlabelctl(8) is needed.

           Example:

               [Address]
               NetLabel=system_u:object_r:localnet_peer_t:s0

           With the example rules applying for interface "eth0", when the interface is configured
           with an IPv4 address of 10.0.0.123/8, systemd-networkd performs the equivalent of
           netlabelctl operation

               netlabelctl unlbl add interface eth0 address:10.0.0.0/8 label:system_u:object_r:localnet_peer_t:s0

           and the reverse operation when the IPv4 address is deconfigured. The configuration can
           be used with LSM rules; in case of SELinux to allow a SELinux domain to receive data
           from objects of SELinux "peer" class. For example:

               type localnet_peer_t;
               allow my_server_t localnet_peer_t:peer recv;

           The effect of the above configuration and rules (in absence of other rules as may be
           the case) is to only allow "my_server_t" (and nothing else) to receive data from local
           subnet 10.0.0.0/8 of interface "eth0".

[NEIGHBOR] SECTION OPTIONS

       A [Neighbor] section accepts the following keys. The neighbor section adds a permanent,
       static entry to the neighbor table (IPv6) or ARP table (IPv4) for the given hardware
       address on the links matched for the network. Specify several [Neighbor] sections to
       configure several static neighbors.

       Address=
           The IP address of the neighbor.

       LinkLayerAddress=
           The link layer address (MAC address or IP address) of the neighbor.

[IPV6ADDRESSLABEL] SECTION OPTIONS

       An [IPv6AddressLabel] section accepts the following keys. Specify several
       [IPv6AddressLabel] sections to configure several address labels. IPv6 address labels are
       used for address selection. See RFC 3484[17]. Precedence is managed by userspace, and only
       the label itself is stored in the kernel.

       Label=
           The label for the prefix, an unsigned integer in the range 0...4294967294. 0xffffffff
           is reserved. This setting is mandatory.

       Prefix=
           IPv6 prefix is an address with a prefix length, separated by a slash "/" character.
           This setting is mandatory.

[ROUTINGPOLICYRULE] SECTION OPTIONS

       An [RoutingPolicyRule] section accepts the following settings. Specify several
       [RoutingPolicyRule] sections to configure several rules.

       TypeOfService=
           Takes a number between 0 and 255 that specifies the type of service to match.

       From=
           Specifies the source address prefix to match. Possibly followed by a slash and the
           prefix length.

       To=
           Specifies the destination address prefix to match. Possibly followed by a slash and
           the prefix length.

       FirewallMark=
           Specifies the iptables firewall mark value to match (a number in the range
           1...4294967295). Optionally, the firewall mask (also a number between 1...4294967295)
           can be suffixed with a slash ("/"), e.g., "7/255".

       Table=
           Specifies the routing table identifier to look up if the rule selector matches. Takes
           one of predefined names "default", "main", and "local", and names defined in
           RouteTable= in networkd.conf(5), or a number between 1 and 4294967295. Defaults to
           "main".

       Priority=
           Specifies the priority of this rule.  Priority= is an integer in the range
           0...4294967295. Higher number means lower priority, and rules get processed in order
           of increasing number. Defaults to unset, and the kernel will pick a value dynamically.

       IncomingInterface=
           Specifies incoming device to match. If the interface is loopback, the rule only
           matches packets originating from this host.

       OutgoingInterface=
           Specifies the outgoing device to match. The outgoing interface is only available for
           packets originating from local sockets that are bound to a device.

       SourcePort=
           Specifies the source IP port or IP port range match in forwarding information base
           (FIB) rules. A port range is specified by the lower and upper port separated by a
           dash. Defaults to unset.

       DestinationPort=
           Specifies the destination IP port or IP port range match in forwarding information
           base (FIB) rules. A port range is specified by the lower and upper port separated by a
           dash. Defaults to unset.

       IPProtocol=
           Specifies the IP protocol to match in forwarding information base (FIB) rules. Takes
           IP protocol name such as "tcp", "udp" or "sctp", or IP protocol number such as "6" for
           "tcp" or "17" for "udp". Defaults to unset.

       InvertRule=
           A boolean. Specifies whether the rule is to be inverted. Defaults to false.

       Family=
           Takes a special value "ipv4", "ipv6", or "both". By default, the address family is
           determined by the address specified in To= or From=. If neither To= nor From= are
           specified, then defaults to "ipv4".

       User=
           Takes a username, a user ID, or a range of user IDs separated by a dash. Defaults to
           unset.

       SuppressPrefixLength=
           Takes a number N in the range 0...128 and rejects routing decisions that have a prefix
           length of N or less. Defaults to unset.

       SuppressInterfaceGroup=
           Takes an integer in the range 0...2147483647 and rejects routing decisions that have
           an interface with the same group id. It has the same meaning as suppress_ifgroup in ip
           rule. Defaults to unset.

       Type=
           Specifies Routing Policy Database (RPDB) rule type. Takes one of "blackhole",
           "unreachable" or "prohibit".

[NEXTHOP] SECTION OPTIONS

       The [NextHop] section is used to manipulate entries in the kernel's "nexthop" tables. The
       [NextHop] section accepts the following settings. Specify several [NextHop] sections to
       configure several hops.

       Id=
           The id of the next hop. Takes an integer in the range 1...4294967295. If unspecified,
           then automatically chosen by kernel.

       Gateway=
           As in the [Network] section.

       Family=
           Takes one of the special values "ipv4" or "ipv6". By default, the family is determined
           by the address specified in Gateway=. If Gateway= is not specified, then defaults to
           "ipv4".

       OnLink=
           Takes a boolean. If set to true, the kernel does not have to check if the gateway is
           reachable directly by the current machine (i.e., attached to the local network), so
           that we can insert the nexthop in the kernel table without it being complained about.
           Defaults to "no".

       Blackhole=
           Takes a boolean. If enabled, packets to the corresponding routes are discarded
           silently, and Gateway= cannot be specified. Defaults to "no".

       Group=
           Takes a whitespace separated list of nexthop IDs. Each ID must be in the range
           1...4294967295. Optionally, each nexthop ID can take a weight after a colon
           ("id[:weight]"). The weight must be in the range 1...255. If the weight is not
           specified, then it is assumed that the weight is 1. This setting cannot be specified
           with Gateway=, Family=, Blackhole=. This setting can be specified multiple times. If
           an empty string is assigned, then the all previous assignments are cleared. Defaults
           to unset.

[ROUTE] SECTION OPTIONS

       The [Route] section accepts the following settings. Specify several [Route] sections to
       configure several routes.

       Gateway=
           Takes the gateway address or the special values "_dhcp4" and "_ipv6ra". If "_dhcp4" or
           "_ipv6ra" is set, then the gateway address provided by DHCPv4 or IPv6 RA is used.

       GatewayOnLink=
           Takes a boolean. If set to true, the kernel does not have to check if the gateway is
           reachable directly by the current machine (i.e., attached to the local network), so
           that we can insert the route in the kernel table without it being complained about.
           Defaults to "no".

       Destination=
           The destination prefix of the route. Possibly followed by a slash and the prefix
           length. If omitted, a full-length host route is assumed.

       Source=
           The source prefix of the route. Possibly followed by a slash and the prefix length. If
           omitted, a full-length host route is assumed.

       Metric=
           The metric of the route. Takes an unsigned integer in the range 0...4294967295.
           Defaults to unset, and the kernel's default will be used.

       IPv6Preference=
           Specifies the route preference as defined in RFC 4191[18] for Router Discovery
           messages. Which can be one of "low" the route has a lowest priority, "medium" the
           route has a default priority or "high" the route has a highest priority.

       Scope=
           The scope of the IPv4 route, which can be "global", "site", "link", "host", or
           "nowhere":

           •   "global" means the route can reach hosts more than one hop away.

           •   "site" means an interior route in the local autonomous system.

           •   "link" means the route can only reach hosts on the local network (one hop away).

           •   "host" means the route will not leave the local machine (used for internal
               addresses like 127.0.0.1).

           •   "nowhere" means the destination doesn't exist.

           For IPv4 route, defaults to "host" if Type= is "local" or "nat", and "link" if Type=
           is "broadcast", "multicast", "anycast", or "unicast". In other cases, defaults to
           "global". The value is not used for IPv6.

       PreferredSource=
           The preferred source address of the route. The address must be in the format described
           in inet_pton(3).

       Table=
           The table identifier for the route. Takes one of predefined names "default", "main",
           and "local", and names defined in RouteTable= in networkd.conf(5), or a number between
           1 and 4294967295. The table can be retrieved using ip route show table num. If unset
           and Type= is "local", "broadcast", "anycast", or "nat", then "local" is used. In other
           cases, defaults to "main".

       Protocol=
           The protocol identifier for the route. Takes a number between 0 and 255 or the special
           values "kernel", "boot", "static", "ra" and "dhcp". Defaults to "static".

       Type=
           Specifies the type for the route. Takes one of "unicast", "local", "broadcast",
           "anycast", "multicast", "blackhole", "unreachable", "prohibit", "throw", "nat", and
           "xresolve". If "unicast", a regular route is defined, i.e. a route indicating the path
           to take to a destination network address. If "blackhole", packets to the defined route
           are discarded silently. If "unreachable", packets to the defined route are discarded
           and the ICMP message "Host Unreachable" is generated. If "prohibit", packets to the
           defined route are discarded and the ICMP message "Communication Administratively
           Prohibited" is generated. If "throw", route lookup in the current routing table will
           fail and the route selection process will return to Routing Policy Database (RPDB).
           Defaults to "unicast".

       InitialCongestionWindow=
           The TCP initial congestion window is used during the start of a TCP connection. During
           the start of a TCP session, when a client requests a resource, the server's initial
           congestion window determines how many packets will be sent during the initial burst of
           data without waiting for acknowledgement. Takes a number between 1 and 1023. Note that
           100 is considered an extremely large value for this option. When unset, the kernel's
           default (typically 10) will be used.

       InitialAdvertisedReceiveWindow=
           The TCP initial advertised receive window is the amount of receive data (in bytes)
           that can initially be buffered at one time on a connection. The sending host can send
           only that amount of data before waiting for an acknowledgment and window update from
           the receiving host. Takes a number between 1 and 1023. Note that 100 is considered an
           extremely large value for this option. When unset, the kernel's default will be used.

       QuickAck=
           Takes a boolean. When true, the TCP quick ACK mode for the route is enabled. When
           unset, the kernel's default will be used.

       FastOpenNoCookie=
           Takes a boolean. When true enables TCP fastopen without a cookie on a per-route basis.
           When unset, the kernel's default will be used.

       TTLPropagate=
           Takes a boolean. When true enables TTL propagation at Label Switched Path (LSP)
           egress. When unset, the kernel's default will be used.

       MTUBytes=
           The maximum transmission unit in bytes to set for the route. The usual suffixes K, M,
           G, are supported and are understood to the base of 1024.

       TCPAdvertisedMaximumSegmentSize=
           Specifies the Path MSS (in bytes) hints given on TCP layer. The usual suffixes K, M,
           G, are supported and are understood to the base of 1024. An unsigned integer in the
           range 1...4294967294. When unset, the kernel's default will be used.

       TCPCongestionControlAlgorithm=
           Specifies the TCP congestion control algorithm for the route. Takes a name of the
           algorithm, e.g.  "bbr", "dctcp", or "vegas". When unset, the kernel's default will be
           used.

       MultiPathRoute=address[@name] [weight]
           Configures multipath route. Multipath routing is the technique of using multiple
           alternative paths through a network. Takes gateway address. Optionally, takes a
           network interface name or index separated with "@", and a weight in 1..256 for this
           multipath route separated with whitespace. This setting can be specified multiple
           times. If an empty string is assigned, then the all previous assignments are cleared.

       NextHop=
           Specifies the nexthop id. Takes an unsigned integer in the range 1...4294967295. If
           set, the corresponding [NextHop] section must be configured. Defaults to unset.

[DHCPV4] SECTION OPTIONS

       The [DHCPv4] section configures the DHCPv4 client, if it is enabled with the DHCP= setting
       described above:

       SendHostname=
           When true (the default), the machine's hostname (or the value specified with
           Hostname=, described below) will be sent to the DHCP server. Note that the hostname
           must consist only of 7-bit ASCII lower-case characters and no spaces or dots, and be
           formatted as a valid DNS domain name. Otherwise, the hostname is not sent even if this
           option is true.

       Hostname=
           Use this value for the hostname which is sent to the DHCP server, instead of machine's
           hostname. Note that the specified hostname must consist only of 7-bit ASCII lower-case
           characters and no spaces or dots, and be formatted as a valid DNS domain name.

       MUDURL=
           When configured, the specified Manufacturer Usage Description (MUD) URL will be sent
           to the DHCPv4 server. Takes a URL of length up to 255 characters. A superficial
           verification that the string is a valid URL will be performed. DHCPv4 clients are
           intended to have at most one MUD URL associated with them. See RFC 8520[19].

           MUD is an embedded software standard defined by the IETF that allows IoT device makers
           to advertise device specifications, including the intended communication patterns for
           their device when it connects to the network. The network can then use this to author
           a context-specific access policy, so the device functions only within those
           parameters.

       ClientIdentifier=
           The DHCPv4 client identifier to use. Takes one of mac, duid or duid-only. If set to
           mac, the MAC address of the link is used. If set to duid, an RFC4361-compliant Client
           ID, which is the combination of IAID and DUID (see below), is used. If set to
           duid-only, only DUID is used, this may not be RFC compliant, but some setups may
           require to use this. Defaults to duid.

       VendorClassIdentifier=
           The vendor class identifier used to identify vendor type and configuration.

       UserClass=
           A DHCPv4 client can use UserClass option to identify the type or category of user or
           applications it represents. The information contained in this option is a string that
           represents the user class of which the client is a member. Each class sets an
           identifying string of information to be used by the DHCP service to classify clients.
           Takes a whitespace-separated list of strings.

       DUIDType=
           Override the global DUIDType= setting for this network. See networkd.conf(5) for a
           description of possible values.

       DUIDRawData=
           Override the global DUIDRawData= setting for this network. See networkd.conf(5) for a
           description of possible values.

       IAID=
           The DHCP Identity Association Identifier (IAID) for the interface, a 32-bit unsigned
           integer.

       Anonymize=
           Takes a boolean. When true, the options sent to the DHCP server will follow the RFC
           7844[20] (Anonymity Profiles for DHCP Clients) to minimize disclosure of identifying
           information. Defaults to false.

           This option should only be set to true when MACAddressPolicy= is set to random (see
           systemd.link(5)).

           When true, SendHostname=, ClientIdentifier=, VendorClassIdentifier=, UserClass=,
           RequestOptions=, SendOption=, SendVendorOption=, and MUDURL= are ignored.

           With this option enabled DHCP requests will mimic those generated by Microsoft
           Windows, in order to reduce the ability to fingerprint and recognize installations.
           This means DHCP request sizes will grow and lease data will be more comprehensive than
           normally, though most of the requested data is not actually used.

       RequestOptions=
           Sets request options to be sent to the server in the DHCPv4 request options list. A
           whitespace-separated list of integers in the range 1...254. Defaults to unset.

       SendOption=
           Send an arbitrary raw option in the DHCPv4 request. Takes a DHCP option number, data
           type and data separated with a colon ("option:type:value"). The option number must be
           an integer in the range 1...254. The type takes one of "uint8", "uint16", "uint32",
           "ipv4address", or "string". Special characters in the data string may be escaped using
           C-style escapes[21]. This setting can be specified multiple times. If an empty string
           is specified, then all options specified earlier are cleared. Defaults to unset.

       SendVendorOption=
           Send an arbitrary vendor option in the DHCPv4 request. Takes a DHCP option number,
           data type and data separated with a colon ("option:type:value"). The option number
           must be an integer in the range 1...254. The type takes one of "uint8", "uint16",
           "uint32", "ipv4address", or "string". Special characters in the data string may be
           escaped using C-style escapes[21]. This setting can be specified multiple times. If an
           empty string is specified, then all options specified earlier are cleared. Defaults to
           unset.

       IPServiceType=
           Takes one of the special values "none", "CS6", or "CS4". When "none" no IP service
           type is set to the packet sent from the DHCPv4 client. When "CS6" (network control) or
           "CS4" (realtime), the corresponding service type will be set. Defaults to "CS6".

       SocketPriority=
           The Linux socket option SO_PRIORITY applied to the raw IP socket used for initial
           DHCPv4 messages. Unset by default. Usual values range from 0 to 6. More details about
           SO_PRIORITY socket option in socket(7). Can be used in conjunction with [VLAN] section
           EgressQOSMaps= setting of .netdev file to set the 802.1Q VLAN ethernet tagged header
           priority, see systemd.netdev(5).

       Label=
           Specifies the label for the IPv4 address received from the DHCP server. The label must
           be a 7-bit ASCII string with a length of 1...15 characters. Defaults to unset.

       UseDNS=
           When true (the default), the DNS servers received from the DHCP server will be used.

           This corresponds to the nameserver option in resolv.conf(5).

       RoutesToDNS=
           When true, the routes to the DNS servers received from the DHCP server will be
           configured. When UseDNS= is disabled, this setting is ignored. Defaults to true.

       UseNTP=
           When true (the default), the NTP servers received from the DHCP server will be used by
           systemd-timesyncd.service.

       RoutesToNTP=
           When true, the routes to the NTP servers received from the DHCP server will be
           configured. When UseNTP= is disabled, this setting is ignored. Defaults to true.

       UseSIP=
           When true (the default), the SIP servers received from the DHCP server will be
           collected and made available to client programs.

       UseMTU=
           When true, the interface maximum transmission unit from the DHCP server will be used
           on the current link. If MTUBytes= is set, then this setting is ignored. Defaults to
           false.

           Note, some drivers will reset the interfaces if the MTU is changed. For such
           interfaces, please try to use IgnoreCarrierLoss= with a short timespan, e.g.  "3
           seconds".

       UseHostname=
           When true (the default), the hostname received from the DHCP server will be set as the
           transient hostname of the system.

       UseDomains=
           Takes a boolean, or the special value route. When true, the domain name received from
           the DHCP server will be used as DNS search domain over this link, similarly to the
           effect of the Domains= setting. If set to route, the domain name received from the
           DHCP server will be used for routing DNS queries only, but not for searching,
           similarly to the effect of the Domains= setting when the argument is prefixed with
           "~". Defaults to true on Ubuntu.

           It is recommended to enable this option only on trusted networks, as setting this
           affects resolution of all hostnames, in particular of single-label names. It is
           generally safer to use the supplied domain only as routing domain, rather than as
           search domain, in order to not have it affect local resolution of single-label names.

           When set to true, this setting corresponds to the domain option in resolv.conf(5).

       UseRoutes=
           When true (the default), the static routes will be requested from the DHCP server and
           added to the routing table with a metric of 1024, and a scope of global, link or host,
           depending on the route's destination and gateway. If the destination is on the local
           host, e.g., 127.x.x.x, or the same as the link's own address, the scope will be set to
           host. Otherwise if the gateway is null (a direct route), a link scope will be used.
           For anything else, scope defaults to global.

       RouteMetric=
           Set the routing metric for routes specified by the DHCP server (including the prefix
           route added for the specified prefix). Takes an unsigned integer in the range
           0...4294967295. Defaults to 1024.

       RouteTable=num
           The table identifier for DHCP routes. Takes one of predefined names "default", "main",
           and "local", and names defined in RouteTable= in networkd.conf(5), or a number between
           1...4294967295.

           When used in combination with VRF=, the VRF's routing table is used when this
           parameter is not specified.

       RouteMTUBytes=
           Specifies the MTU for the DHCP routes. Please see the [Route] section for further
           details.

       QuickAck=
           Takes a boolean. When true, the TCP quick ACK mode is enabled for the routes
           configured by the acquired DHCPv4 lease. When unset, the kernel's default will be
           used.

       UseGateway=
           When true, the gateway will be requested from the DHCP server and added to the routing
           table with a metric of 1024, and a scope of link. When unset, the value specified with
           UseRoutes= is used.

       UseTimezone=
           When true, the timezone received from the DHCP server will be set as timezone of the
           local system. Defaults to false.

       Use6RD=
           When true, subnets of the received IPv6 prefix are assigned to downstream interfaces
           which enables DHCPPrefixDelegation=. See also DHCPPrefixDelegation= in the [Network]
           section, the [DHCPPrefixDelegation] section, and RFC 5969[22]. Defaults to false.

       FallbackLeaseLifetimeSec=
           Allows one to set DHCPv4 lease lifetime when DHCPv4 server does not send the lease
           lifetime. Takes one of "forever" or "infinity". If specified, the acquired address
           never expires. Defaults to unset.

       RequestBroadcast=
           Request the server to use broadcast messages before the IP address has been
           configured. This is necessary for devices that cannot receive RAW packets, or that
           cannot receive packets at all before an IP address has been configured. On the other
           hand, this must not be enabled on networks where broadcasts are filtered out.

       MaxAttempts=
           Specifies how many times the DHCPv4 client configuration should be attempted. Takes a
           number or "infinity". Defaults to "infinity". Note that the time between retries is
           increased exponentially, up to approximately one per minute, so the network will not
           be overloaded even if this number is high. The default is suitable in most
           circumstances.

       ListenPort=
           Set the port from which the DHCP client packets originate.

       DenyList=
           A whitespace-separated list of IPv4 addresses. Each address can optionally take a
           prefix length after "/". DHCP offers from servers in the list are rejected. Note that
           if AllowList= is configured then DenyList= is ignored.

       AllowList=
           A whitespace-separated list of IPv4 addresses. Each address can optionally take a
           prefix length after "/". DHCP offers from servers in the list are accepted.

       SendRelease=
           When true, the DHCPv4 client sends a DHCP release packet when it stops. Defaults to
           true.

       SendDecline=
           A boolean. When true, systemd-networkd performs IPv4 Duplicate Address Detection to
           the acquired address by the DHCPv4 client. If duplicate is detected, the DHCPv4 client
           rejects the address by sending a DHCPDECLINE packet to the DHCP server, and tries to
           obtain an IP address again. See RFC 5227[11]. Defaults to false.

       NetLabel=
           This applies the NetLabel for the addresses received with DHCP, like NetLabel= in
           [Address] section applies it to statically configured addresses. See NetLabel= in
           [Address] section for more details.

[DHCPV6] SECTION OPTIONS

       The [DHCPv6] section configures the DHCPv6 client, if it is enabled with the DHCP= setting
       described above, or invoked by the IPv6 Router Advertisement:

       MUDURL=, IAID=, DUIDType=, DUIDRawData=, RequestOptions=
           As in the [DHCPv4] section.

       SendOption=
           As in the [DHCPv4] section, however because DHCPv6 uses 16-bit fields to store option
           numbers, the option number is an integer in the range 1...65536.

       SendVendorOption=
           Send an arbitrary vendor option in the DHCPv6 request. Takes an enterprise identifier,
           DHCP option number, data type, and data separated with a colon ("enterprise
           identifier:option:type:value"). Enterprise identifier is an unsigned integer in the
           range 1...4294967294. The option number must be an integer in the range 1...254. Data
           type takes one of "uint8", "uint16", "uint32", "ipv4address", "ipv6address", or
           "string". Special characters in the data string may be escaped using C-style
           escapes[21]. This setting can be specified multiple times. If an empty string is
           specified, then all options specified earlier are cleared. Defaults to unset.

       UserClass=
           A DHCPv6 client can use User Class option to identify the type or category of user or
           applications it represents. The information contained in this option is a string that
           represents the user class of which the client is a member. Each class sets an
           identifying string of information to be used by the DHCP service to classify clients.
           Special characters in the data string may be escaped using C-style escapes[21]. This
           setting can be specified multiple times. If an empty string is specified, then all
           options specified earlier are cleared. Takes a whitespace-separated list of strings.
           Note that currently NUL bytes are not allowed.

       VendorClass=
           A DHCPv6 client can use VendorClass option to identify the vendor that manufactured
           the hardware on which the client is running. The information contained in the data
           area of this option is contained in one or more opaque fields that identify details of
           the hardware configuration. Takes a whitespace-separated list of strings.

       PrefixDelegationHint=
           Takes an IPv6 address with prefix length in the same format as the Address= in the
           [Network] section. The DHCPv6 client will include a prefix hint in the DHCPv6
           solicitation sent to the server. The prefix length must be in the range 1...128.
           Defaults to unset.

       RapidCommit=
           Takes a boolean. The DHCPv6 client can obtain configuration parameters from a DHCPv6
           server through a rapid two-message exchange (solicit and reply). When the rapid commit
           option is set by both the DHCPv6 client and the DHCPv6 server, the two-message
           exchange is used. Otherwise, the four-message exchange (solicit, advertise, request,
           and reply) is used. The two-message exchange provides faster client configuration. See
           RFC 3315[23] for details. Defaults to true, and the two-message exchange will be used
           if the server support it.

       UseAddress=
           When true (the default), the IP addresses provided by the DHCPv6 server will be
           assigned.

       UseDelegatedPrefix=
           When true (the default), the client will request the DHCPv6 server to delegate
           prefixes. If the server provides prefixes to be delegated, then subnets of the
           prefixes are assigned to the interfaces that have DHCPPrefixDelegation=yes. See also
           the DHCPPrefixDelegation= setting in the [Network] section, settings in the
           [DHCPPrefixDelegation] section, and RFC 8415[24].

       UseDNS=, UseNTP=, UseHostname=, UseDomains=, NetLabel=, SendRelease=
           As in the [DHCPv4] section.

       WithoutRA=
           Allows DHCPv6 client to start without router advertisements's "managed" or "other
           configuration" flag. Takes one of "no", "solicit", or "information-request". If this
           is not specified, "solicit" is used when DHCPPrefixDelegation= is enabled and
           UplinkInterface=:self is specified in the [DHCPPrefixDelegation] section. Otherwise,
           defaults to "no", and the DHCPv6 client will be started when an RA is received. See
           also the DHCPv6Client= setting in the [IPv6AcceptRA] section.

[DHCPPREFIXDELEGATION] SECTION OPTIONS

       The [DHCPPrefixDelegation] section configures subnet prefixes of the delegated prefixes
       acquired by a DHCPv6 client or by a DHCPv4 client through the 6RD option on another
       interface. The settings in this section are used only when the DHCPPrefixDelegation=
       setting in the [Network] section is enabled.

       UplinkInterface=
           Specifies the name or the index of the uplink interface, or one of the special values
           ":self" and ":auto". When ":self", the interface itself is considered the uplink
           interface, and WithoutRA=solicit is implied if the setting is not explicitly
           specified. When ":auto", the first link which acquired prefixes to be delegated from
           the DHCPv6 or DHCPv4 server is selected. Defaults to ":auto".

       SubnetId=
           Configure a specific subnet ID on the interface from a (previously) received prefix
           delegation. You can either set "auto" (the default) or a specific subnet ID (as
           defined in RFC 4291[25], section 2.5.4), in which case the allowed value is
           hexadecimal, from 0 to 0x7fffffffffffffff inclusive.

       Announce=
           Takes a boolean. When enabled, and IPv6SendRA= in [Network] section is enabled, the
           delegated prefixes are distributed through the IPv6 Router Advertisement. This setting
           will be ignored when the DHCPPrefixDelegation= setting is enabled on the upstream
           interface. Defaults to yes.

       Assign=
           Takes a boolean. Specifies whether to add an address from the delegated prefixes which
           are received from the WAN interface by the DHCPv6 Prefix Delegation. When true (on LAN
           interface), the EUI-64 algorithm will be used by default to form an interface
           identifier from the delegated prefixes. See also Token= setting below. Defaults to
           yes.

       Token=
           Specifies an optional address generation mode for assigning an address in each
           delegated prefix. This accepts the same syntax as Token= in the [IPv6AcceptRA]
           section. If Assign= is set to false, then this setting will be ignored. Defaults to
           unset, which means the EUI-64 algorithm will be used.

       ManageTemporaryAddress=
           As in the [Address] section, but defaults to true.

       RouteMetric=
           The metric of the route to the delegated prefix subnet. Takes an unsigned integer in
           the range 0...4294967295. When set to 0, the kernel's default value is used. Defaults
           to 256.

       NetLabel=
           This applies the NetLabel for the addresses received with DHCP, like NetLabel= in
           [Address] section applies it to statically configured addresses. See NetLabel= in
           [Address] section for more details.

[IPV6ACCEPTRA] SECTION OPTIONS

       The [IPv6AcceptRA] section configures the IPv6 Router Advertisement (RA) client, if it is
       enabled with the IPv6AcceptRA= setting described above:

       Token=
           Specifies an optional address generation mode for the Stateless Address
           Autoconfiguration (SLAAC). The following values are supported:

           eui64
               The EUI-64 algorithm will be used to generate an address for that prefix. Only
               supported by Ethernet or InfiniBand interfaces.

           static:ADDRESS
               An IPv6 address must be specified after a colon (":"), and the lower bits of the
               supplied address are combined with the upper bits of a prefix received in a Router
               Advertisement (RA) message to form a complete address. Note that if multiple
               prefixes are received in an RA message, or in multiple RA messages, addresses will
               be formed from each of them using the supplied address. This mode implements SLAAC
               but uses a static interface identifier instead of an identifier generated by using
               the EUI-64 algorithm. Because the interface identifier is static, if Duplicate
               Address Detection detects that the computed address is a duplicate (in use by
               another node on the link), then this mode will fail to provide an address for that
               prefix. If an IPv6 address without mode is specified, then "static" mode is
               assumed.

           prefixstable[:ADDRESS][,UUID]
               The algorithm specified in RFC 7217[26] will be used to generate interface
               identifiers. This mode can optionally take an IPv6 address separated with a colon
               (":"). If an IPv6 address is specified, then an interface identifier is generated
               only when a prefix received in an RA message matches the supplied address.

               This mode can also optionally take a non-null UUID in the format which
               sd_id128_from_string() accepts, e.g.  "86b123b969ba4b7eb8b3d8605123525a" or
               "86b123b9-69ba-4b7e-b8b3-d8605123525a". If a UUID is specified, the value is used
               as the secret key to generate interface identifiers. If not specified, then an
               application specific ID generated with the system's machine-ID will be used as the
               secret key. See sd-id128(3), sd_id128_from_string(3), and sd_id128_get_machine(3).

               Note that the "prefixstable" algorithm uses both the interface name and MAC
               address as input to the hash to compute the interface identifier, so if either of
               those are changed the resulting interface identifier (and address) will be
               changed, even if the prefix received in the RA message has not been changed.

           If no address generation mode is specified (which is the default), or a received
           prefix does not match any of the addresses provided in "prefixstable" mode, then the
           EUI-64 algorithm will be used for Ethernet or InfiniBand interfaces, otherwise
           "prefixstable" will be used to form an interface identifier for that prefix.

           This setting can be specified multiple times. If an empty string is assigned, then the
           all previous assignments are cleared.

           Examples:

               Token=eui64
               Token=::1a:2b:3c:4d
               Token=static:::1a:2b:3c:4d
               Token=prefixstable
               Token=prefixstable:2002:da8:1::

       UseDNS=
           When true (the default), the DNS servers received in the Router Advertisement will be
           used.

           This corresponds to the nameserver option in resolv.conf(5).

       UseDomains=
           Takes a boolean, or the special value "route". When true, the domain name received via
           IPv6 Router Advertisement (RA) will be used as DNS search domain over this link,
           similarly to the effect of the Domains= setting. If set to "route", the domain name
           received via IPv6 RA will be used for routing DNS queries only, but not for searching,
           similarly to the effect of the Domains= setting when the argument is prefixed with
           "~". Defaults to true on Ubuntu.

           It is recommended to enable this option only on trusted networks, as setting this
           affects resolution of all hostnames, in particular of single-label names. It is
           generally safer to use the supplied domain only as routing domain, rather than as
           search domain, in order to not have it affect local resolution of single-label names.

           When set to true, this setting corresponds to the domain option in resolv.conf(5).

       RouteTable=num
           The table identifier for the routes received in the Router Advertisement. Takes one of
           predefined names "default", "main", and "local", and names defined in RouteTable= in
           networkd.conf(5), or a number between 1...4294967295.

           When used in combination with VRF=, the VRF's routing table is used when this
           parameter is not specified.

       RouteMetric=
           Set the routing metric for the routes received in the Router Advertisement. Takes an
           unsigned integer in the range 0...4294967295, or three unsigned integer separated with
           ":", in that case the first one is used when the router preference is high, the second
           is for medium preference, and the last is for low preference ("high:medium:low").
           Defaults to "512:1024:2048".

       QuickAck=
           Takes a boolean. When true, the TCP quick ACK mode is enabled for the routes
           configured by the received RAs. When unset, the kernel's default will be used.

       UseMTU=
           Takes a boolean. When true, the MTU received in the Router Advertisement will be used.
           Defaults to true.

       UseGateway=
           When true (the default), the router address will be configured as the default gateway.

       UseRoutePrefix=
           When true (the default), the routes corresponding to the route prefixes received in
           the Router Advertisement will be configured.

       UseAutonomousPrefix=
           When true (the default), the autonomous prefix received in the Router Advertisement
           will be used and take precedence over any statically configured ones.

       UseOnLinkPrefix=
           When true (the default), the onlink prefix received in the Router Advertisement will
           be used and takes precedence over any statically configured ones.

       RouterDenyList=
           A whitespace-separated list of IPv6 router addresses. Each address can optionally take
           a prefix length after "/". Any information advertised by the listed router is ignored.

       RouterAllowList=
           A whitespace-separated list of IPv6 router addresses. Each address can optionally take
           a prefix length after "/". Only information advertised by the listed router is
           accepted. Note that if RouterAllowList= is configured then RouterDenyList= is ignored.

       PrefixDenyList=
           A whitespace-separated list of IPv6 prefixes. Each prefix can optionally take its
           prefix length after "/". IPv6 prefixes supplied via router advertisements in the list
           are ignored.

       PrefixAllowList=
           A whitespace-separated list of IPv6 prefixes. Each prefix can optionally take its
           prefix length after "/". IPv6 prefixes supplied via router advertisements in the list
           are allowed. Note that if PrefixAllowList= is configured then PrefixDenyList= is
           ignored.

       RouteDenyList=
           A whitespace-separated list of IPv6 route prefixes. Each prefix can optionally take
           its prefix length after "/". IPv6 route prefixes supplied via router advertisements in
           the list are ignored.

       RouteAllowList=
           A whitespace-separated list of IPv6 route prefixes. Each prefix can optionally take
           its prefix length after "/". IPv6 route prefixes supplied via router advertisements in
           the list are allowed. Note that if RouteAllowList= is configured then RouteDenyList=
           is ignored.

       DHCPv6Client=
           Takes a boolean, or the special value "always". When true, the DHCPv6 client will be
           started in "solicit" mode if the RA has the "managed" flag or "information-request"
           mode if the RA lacks the "managed" flag but has the "other configuration" flag. If set
           to "always", the DHCPv6 client will be started in "solicit" mode when an RA is
           received, even if neither the "managed" nor the "other configuration" flag is set in
           the RA. This will be ignored when WithoutRA= in the [DHCPv6] section is enabled, or
           UplinkInterface=:self in the [DHCPPrefixDelegation] section is specified. Defaults to
           true.

       NetLabel=
           This applies the NetLabel for the addresses received with RA, like NetLabel= in
           [Address] section applies it to statically configured addresses. See NetLabel= in
           [Address] section for more details.

[DHCPSERVER] SECTION OPTIONS

       The [DHCPServer] section contains settings for the DHCP server, if enabled via the
       DHCPServer= option described above:

       ServerAddress=
           Specifies server address for the DHCP server. Takes an IPv4 address with prefix
           length, for example 192.168.0.1/24. This setting may be useful when the link on which
           the DHCP server is running has multiple static addresses. When unset, one of static
           addresses in the link will be automatically selected. Defaults to unset.

       PoolOffset=, PoolSize=
           Configures the pool of addresses to hand out. The pool is a contiguous sequence of IP
           addresses in the subnet configured for the server address, which does not include the
           subnet nor the broadcast address.  PoolOffset= takes the offset of the pool from the
           start of subnet, or zero to use the default value.  PoolSize= takes the number of IP
           addresses in the pool or zero to use the default value. By default, the pool starts at
           the first address after the subnet address and takes up the rest of the subnet,
           excluding the broadcast address. If the pool includes the server address (the
           default), this is reserved and not handed out to clients.

       DefaultLeaseTimeSec=, MaxLeaseTimeSec=
           Control the default and maximum DHCP lease time to pass to clients. These settings
           take time values in seconds or another common time unit, depending on the suffix. The
           default lease time is used for clients that did not ask for a specific lease time. If
           a client asks for a lease time longer than the maximum lease time, it is automatically
           shortened to the specified time. The default lease time defaults to 1h, the maximum
           lease time to 12h. Shorter lease times are beneficial if the configuration data in
           DHCP leases changes frequently and clients shall learn the new settings with shorter
           latencies. Longer lease times reduce the generated DHCP network traffic.

       UplinkInterface=
           Specifies the name or the index of the uplink interface, or one of the special values
           ":none" and ":auto". When emitting DNS, NTP, or SIP servers is enabled but no servers
           are specified, the servers configured in the uplink interface will be emitted. When
           ":auto", the link which has a default gateway with the highest priority will be
           automatically selected. When ":none", no uplink interface will be selected. Defaults
           to ":auto".

       EmitDNS=, DNS=
           EmitDNS= takes a boolean. Configures whether the DHCP leases handed out to clients
           shall contain DNS server information. Defaults to "yes". The DNS servers to pass to
           clients may be configured with the DNS= option, which takes a list of IPv4 addresses,
           or special value "_server_address" which will be converted to the address used by the
           DHCP server.

           If the EmitDNS= option is enabled but no servers configured, the servers are
           automatically propagated from an "uplink" interface that has appropriate servers set.
           The "uplink" interface is determined by the default route of the system with the
           highest priority. Note that this information is acquired at the time the lease is
           handed out, and does not take uplink interfaces into account that acquire DNS server
           information at a later point. If no suitable uplink interface is found the DNS server
           data from /etc/resolv.conf is used. Also, note that the leases are not refreshed if
           the uplink network configuration changes. To ensure clients regularly acquire the most
           current uplink DNS server information, it is thus advisable to shorten the DHCP lease
           time via MaxLeaseTimeSec= described above.

           This setting can be specified multiple times. If an empty string is specified, then
           all DNS servers specified earlier are cleared.

       EmitNTP=, NTP=, EmitSIP=, SIP=, EmitPOP3=, POP3=, EmitSMTP=, SMTP=, EmitLPR=, LPR=
           Similar to the EmitDNS= and DNS= settings described above, these settings configure
           whether and what server information for the indicate protocol shall be emitted as part
           of the DHCP lease. The same syntax, propagation semantics and defaults apply as for
           EmitDNS= and DNS=.

       EmitRouter=, Router=
           The EmitRouter= setting takes a boolean value, and configures whether the DHCP lease
           should contain the router option. The Router= setting takes an IPv4 address, and
           configures the router address to be emitted. When the Router= setting is not
           specified, then the server address will be used for the router option. When the
           EmitRouter= setting is disabled, the Router= setting will be ignored. The EmitRouter=
           setting defaults to true, and the Router= setting defaults to unset.

       EmitTimezone=, Timezone=
           Takes a boolean. Configures whether the DHCP leases handed out to clients shall
           contain timezone information. Defaults to "yes". The Timezone= setting takes a
           timezone string (such as "Europe/Berlin" or "UTC") to pass to clients. If no explicit
           timezone is set, the system timezone of the local host is propagated, as determined by
           the /etc/localtime symlink.

       BootServerAddress=
           Takes an IPv4 address of the boot server used by e.g. PXE boot systems. When
           specified, this address is sent in the siaddr field of the DHCP message header. See
           RFC 2131[27] for more details. Defaults to unset.

       BootServerName=
           Takes a name of the boot server used by e.g. PXE boot systems. When specified, this
           name is sent in the DHCP option 66 ("TFTP server name"). See RFC 2132[28] for more
           details. Defaults to unset.

           Note that typically setting one of BootServerName= or BootServerAddress= is
           sufficient, but both can be set too, if desired.

       BootFilename=
           Takes a path or URL to a file loaded by e.g. a PXE boot loader. When specified, this
           path is sent in the DHCP option 67 ("Bootfile name"). See RFC 2132[28] for more
           details. Defaults to unset.

       SendOption=
           Send a raw option with value via DHCPv4 server. Takes a DHCP option number, data type
           and data ("option:type:value"). The option number is an integer in the range 1...254.
           The type takes one of "uint8", "uint16", "uint32", "ipv4address", "ipv6address", or
           "string". Special characters in the data string may be escaped using C-style
           escapes[21]. This setting can be specified multiple times. If an empty string is
           specified, then all options specified earlier are cleared. Defaults to unset.

       SendVendorOption=
           Send a vendor option with value via DHCPv4 server. Takes a DHCP option number, data
           type and data ("option:type:value"). The option number is an integer in the range
           1...254. The type takes one of "uint8", "uint16", "uint32", "ipv4address", or
           "string". Special characters in the data string may be escaped using C-style
           escapes[21]. This setting can be specified multiple times. If an empty string is
           specified, then all options specified earlier are cleared. Defaults to unset.

       BindToInterface=
           Takes a boolean value. When "yes", DHCP server socket will be bound to its network
           interface and all socket communication will be restricted to this interface. Defaults
           to "yes", except if RelayTarget= is used (see below), in which case it defaults to
           "no".

       RelayTarget=
           Takes an IPv4 address, which must be in the format described in inet_pton(3). Turns
           this DHCP server into a DHCP relay agent. See RFC 1542[29]. The address is the address
           of DHCP server or another relay agent to forward DHCP messages to and from.

       RelayAgentCircuitId=
           Specifies value for Agent Circuit ID suboption of Relay Agent Information option.
           Takes a string, which must be in the format "string:value", where "value" should be
           replaced with the value of the suboption. Defaults to unset (means no Agent Circuit ID
           suboption is generated). Ignored if RelayTarget= is not specified.

       RelayAgentRemoteId=
           Specifies value for Agent Remote ID suboption of Relay Agent Information option. Takes
           a string, which must be in the format "string:value", where "value" should be replaced
           with the value of the suboption. Defaults to unset (means no Agent Remote ID suboption
           is generated). Ignored if RelayTarget= is not specified.

[DHCPSERVERSTATICLEASE] SECTION OPTIONS

       The "[DHCPServerStaticLease]" section configures a static DHCP lease to assign a fixed
       IPv4 address to a specific device based on its MAC address. This section can be specified
       multiple times.

       MACAddress=
           The hardware address of a device to match. This key is mandatory.

       Address=
           The IPv4 address that should be assigned to the device that was matched with
           MACAddress=. This key is mandatory.

[IPV6SENDRA] SECTION OPTIONS

       The [IPv6SendRA] section contains settings for sending IPv6 Router Advertisements and
       whether to act as a router, if enabled via the IPv6SendRA= option described above. IPv6
       network prefixes or routes are defined with one or more [IPv6Prefix] or [IPv6RoutePrefix]
       sections.

       Managed=, OtherInformation=
           Takes a boolean. Controls whether a DHCPv6 server is used to acquire IPv6 addresses on
           the network link when Managed= is set to "true" or if only additional network
           information can be obtained via DHCPv6 for the network link when OtherInformation= is
           set to "true". Both settings default to "false", which means that a DHCPv6 server is
           not being used.

       RouterLifetimeSec=
           Takes a timespan. Configures the IPv6 router lifetime in seconds. The value must be 0
           seconds, or between 4 seconds and 9000 seconds. When set to 0, the host is not acting
           as a router. Defaults to 1800 seconds (30 minutes).

       RouterPreference=
           Configures IPv6 router preference if RouterLifetimeSec= is non-zero. Valid values are
           "high", "medium" and "low", with "normal" and "default" added as synonyms for "medium"
           just to make configuration easier. See RFC 4191[18] for details. Defaults to "medium".

       UplinkInterface=
           Specifies the name or the index of the uplink interface, or one of the special values
           ":none" and ":auto". When emitting DNS servers or search domains is enabled but no
           servers are specified, the servers configured in the uplink interface will be emitted.
           When ":auto", the value specified to the same setting in the [DHCPPrefixDelegation]
           section will be used if DHCPPrefixDelegation= is enabled, otherwise the link which has
           a default gateway with the highest priority will be automatically selected. When
           ":none", no uplink interface will be selected. Defaults to ":auto".

       EmitDNS=, DNS=
           DNS= specifies a list of recursive DNS server IPv6 addresses that are distributed via
           Router Advertisement messages when EmitDNS= is true.  DNS= also takes special value
           "_link_local"; in that case the IPv6 link-local address is distributed. If DNS= is
           empty, DNS servers are read from the [Network] section. If the [Network] section does
           not contain any DNS servers either, DNS servers from the uplink interface specified in
           UplinkInterface= will be used. When EmitDNS= is false, no DNS server information is
           sent in Router Advertisement messages.  EmitDNS= defaults to true.

       EmitDomains=, Domains=
           A list of DNS search domains distributed via Router Advertisement messages when
           EmitDomains= is true. If Domains= is empty, DNS search domains are read from the
           [Network] section. If the [Network] section does not contain any DNS search domains
           either, DNS search domains from the uplink interface specified in UplinkInterface=
           will be used. When EmitDomains= is false, no DNS search domain information is sent in
           Router Advertisement messages.  EmitDomains= defaults to true.

       DNSLifetimeSec=
           Lifetime in seconds for the DNS server addresses listed in DNS= and search domains
           listed in Domains=. Defaults to 3600 seconds (one hour).

[IPV6PREFIX] SECTION OPTIONS

       One or more [IPv6Prefix] sections contain the IPv6 prefixes that are announced via Router
       Advertisements. See RFC 4861[30] for further details.

       AddressAutoconfiguration=, OnLink=
           Takes a boolean to specify whether IPv6 addresses can be autoconfigured with this
           prefix and whether the prefix can be used for onlink determination. Both settings
           default to "true" in order to ease configuration.

       Prefix=
           The IPv6 prefix that is to be distributed to hosts. Similarly to configuring static
           IPv6 addresses, the setting is configured as an IPv6 prefix and its prefix length,
           separated by a "/" character. Use multiple [IPv6Prefix] sections to configure multiple
           IPv6 prefixes since prefix lifetimes, address autoconfiguration and onlink status may
           differ from one prefix to another.

       PreferredLifetimeSec=, ValidLifetimeSec=
           Preferred and valid lifetimes for the prefix measured in seconds.
           PreferredLifetimeSec= defaults to 1800 seconds (30 minutes) and ValidLifetimeSec=
           defaults to 3600 seconds (one hour).

       Assign=
           Takes a boolean. When true, adds an address from the prefix. Default to false.

       Token=
           Specifies an optional address generation mode for assigning an address in each prefix.
           This accepts the same syntax as Token= in the [IPv6AcceptRA] section. If Assign= is
           set to false, then this setting will be ignored. Defaults to unset, which means the
           EUI-64 algorithm will be used.

       RouteMetric=
           The metric of the prefix route. Takes an unsigned integer in the range 0...4294967295.
           When unset or set to 0, the kernel's default value is used. This setting is ignored
           when Assign= is false.

[IPV6ROUTEPREFIX] SECTION OPTIONS

       One or more [IPv6RoutePrefix] sections contain the IPv6 prefix routes that are announced
       via Router Advertisements. See RFC 4191[18] for further details.

       Route=
           The IPv6 route that is to be distributed to hosts. Similarly to configuring static
           IPv6 routes, the setting is configured as an IPv6 prefix routes and its prefix route
           length, separated by a "/" character. Use multiple [IPv6RoutePrefix] sections to
           configure multiple IPv6 prefix routes.

       LifetimeSec=
           Lifetime for the route prefix measured in seconds.  LifetimeSec= defaults to 3600
           seconds (one hour).

[BRIDGE] SECTION OPTIONS

       The [Bridge] section accepts the following keys:

       UnicastFlood=
           Takes a boolean. Controls whether the bridge should flood traffic for which an FDB
           entry is missing and the destination is unknown through this port. When unset, the
           kernel's default will be used.

       MulticastFlood=
           Takes a boolean. Controls whether the bridge should flood traffic for which an MDB
           entry is missing and the destination is unknown through this port. When unset, the
           kernel's default will be used.

       MulticastToUnicast=
           Takes a boolean. Multicast to unicast works on top of the multicast snooping feature
           of the bridge. Which means unicast copies are only delivered to hosts which are
           interested in it. When unset, the kernel's default will be used.

       NeighborSuppression=
           Takes a boolean. Configures whether ARP and ND neighbor suppression is enabled for
           this port. When unset, the kernel's default will be used.

       Learning=
           Takes a boolean. Configures whether MAC address learning is enabled for this port.
           When unset, the kernel's default will be used.

       HairPin=
           Takes a boolean. Configures whether traffic may be sent back out of the port on which
           it was received. When this flag is false, then the bridge will not forward traffic
           back out of the receiving port. When unset, the kernel's default will be used.

       Isolated=
           Takes a boolean. Configures whether this port is isolated or not. Within a bridge,
           isolated ports can only communicate with non-isolated ports. When set to true, this
           port can only communicate with other ports whose Isolated setting is false. When set
           to false, this port can communicate with any other ports. When unset, the kernel's
           default will be used.

       UseBPDU=
           Takes a boolean. Configures whether STP Bridge Protocol Data Units will be processed
           by the bridge port. When unset, the kernel's default will be used.

       FastLeave=
           Takes a boolean. This flag allows the bridge to immediately stop multicast traffic on
           a port that receives an IGMP Leave message. It is only used with IGMP snooping if
           enabled on the bridge. When unset, the kernel's default will be used.

       AllowPortToBeRoot=
           Takes a boolean. Configures whether a given port is allowed to become a root port.
           Only used when STP is enabled on the bridge. When unset, the kernel's default will be
           used.

       ProxyARP=
           Takes a boolean. Configures whether proxy ARP to be enabled on this port. When unset,
           the kernel's default will be used.

       ProxyARPWiFi=
           Takes a boolean. Configures whether proxy ARP to be enabled on this port which meets
           extended requirements by IEEE 802.11 and Hotspot 2.0 specifications. When unset, the
           kernel's default will be used.

       MulticastRouter=
           Configures this port for having multicast routers attached. A port with a multicast
           router will receive all multicast traffic. Takes one of "no" to disable multicast
           routers on this port, "query" to let the system detect the presence of routers,
           "permanent" to permanently enable multicast traffic forwarding on this port, or
           "temporary" to enable multicast routers temporarily on this port, not depending on
           incoming queries. When unset, the kernel's default will be used.

       Cost=
           Sets the "cost" of sending packets of this interface. Each port in a bridge may have a
           different speed and the cost is used to decide which link to use. Faster interfaces
           should have lower costs. It is an integer value between 1 and 65535.

       Priority=
           Sets the "priority" of sending packets on this interface. Each port in a bridge may
           have a different priority which is used to decide which link to use. Lower value means
           higher priority. It is an integer value between 0 to 63. Networkd does not set any
           default, meaning the kernel default value of 32 is used.

[BRIDGEFDB] SECTION OPTIONS

       The [BridgeFDB] section manages the forwarding database table of a port and accepts the
       following keys. Specify several [BridgeFDB] sections to configure several static MAC table
       entries.

       MACAddress=
           As in the [Network] section. This key is mandatory.

       Destination=
           Takes an IP address of the destination VXLAN tunnel endpoint.

       VLANId=
           The VLAN ID for the new static MAC table entry. If omitted, no VLAN ID information is
           appended to the new static MAC table entry.

       VNI=
           The VXLAN Network Identifier (or VXLAN Segment ID) to use to connect to the remote
           VXLAN tunnel endpoint. Takes a number in the range 1...16777215. Defaults to unset.

       AssociatedWith=
           Specifies where the address is associated with. Takes one of "use", "self", "master"
           or "router".  "use" means the address is in use. User space can use this option to
           indicate to the kernel that the fdb entry is in use.  "self" means the address is
           associated with the port drivers fdb. Usually hardware.  "master" means the address is
           associated with master devices fdb.  "router" means the destination address is
           associated with a router. Note that it's valid if the referenced device is a VXLAN
           type device and has route shortcircuit enabled. Defaults to "self".

       OutgoingInterface=
           Specifies the name or index of the outgoing interface for the VXLAN device driver to
           reach the remote VXLAN tunnel endpoint. Defaults to unset.

[BRIDGEMDB] SECTION OPTIONS

       The [BridgeMDB] section manages the multicast membership entries forwarding database table
       of a port and accepts the following keys. Specify several [BridgeMDB] sections to
       configure several permanent multicast membership entries.

       MulticastGroupAddress=
           Specifies the IPv4 or IPv6 multicast group address to add. This setting is mandatory.

       VLANId=
           The VLAN ID for the new entry. Valid ranges are 0 (no VLAN) to 4094. Optional,
           defaults to 0.

[LLDP] SECTION OPTIONS

       The [LLDP] section manages the Link Layer Discovery Protocol (LLDP) and accepts the
       following keys:

       MUDURL=
           When configured, the specified Manufacturer Usage Descriptions (MUD) URL will be sent
           in LLDP packets. The syntax and semantics are the same as for MUDURL= in the [DHCPv4]
           section described above.

           The MUD URLs received via LLDP packets are saved and can be read using the
           sd_lldp_neighbor_get_mud_url() function.

[CAN] SECTION OPTIONS

       The [CAN] section manages the Controller Area Network (CAN bus) and accepts the following
       keys:

       BitRate=
           The bitrate of CAN device in bits per second. The usual SI prefixes (K, M) with the
           base of 1000 can be used here. Takes a number in the range 1...4294967295.

       SamplePoint=
           Optional sample point in percent with one decimal (e.g.  "75%", "87.5%") or permille
           (e.g.  "875‰"). This will be ignored when BitRate= is unspecified.

       TimeQuantaNSec=, PropagationSegment=, PhaseBufferSegment1=, PhaseBufferSegment2=,
       SyncJumpWidth=
           Specifies the time quanta, propagation segment, phase buffer segment 1 and 2, and the
           synchronization jump width, which allow one to define the CAN bit-timing in a hardware
           independent format as proposed by the Bosch CAN 2.0 Specification.  TimeQuantaNSec=
           takes a timespan in nanoseconds.  PropagationSegment=, PhaseBufferSegment1=,
           PhaseBufferSegment2=, and SyncJumpWidth= take number of time quantum specified in
           TimeQuantaNSec= and must be an unsigned integer in the range 0...4294967295. These
           settings except for SyncJumpWidth= will be ignored when BitRate= is specified.

       DataBitRate=, DataSamplePoint=
           The bitrate and sample point for the data phase, if CAN-FD is used. These settings are
           analogous to the BitRate= and SamplePoint= keys.

       DataTimeQuantaNSec=, DataPropagationSegment=, DataPhaseBufferSegment1=,
       DataPhaseBufferSegment2=, DataSyncJumpWidth=
           Specifies the time quanta, propagation segment, phase buffer segment 1 and 2, and the
           synchronization jump width for the data phase, if CAN-FD is used. These settings are
           analogous to the TimeQuantaNSec= or related settings.

       FDMode=
           Takes a boolean. When "yes", CAN-FD mode is enabled for the interface. Note, that a
           bitrate and optional sample point should also be set for the CAN-FD data phase using
           the DataBitRate= and DataSamplePoint= keys, or DataTimeQuanta= and related settings.

       FDNonISO=
           Takes a boolean. When "yes", non-ISO CAN-FD mode is enabled for the interface. When
           unset, the kernel's default will be used.

       RestartSec=
           Automatic restart delay time. If set to a non-zero value, a restart of the CAN
           controller will be triggered automatically in case of a bus-off condition after the
           specified delay time. Subsecond delays can be specified using decimals (e.g.  "0.1s")
           or a "ms" or "us" postfix. Using "infinity" or "0" will turn the automatic restart
           off. By default automatic restart is disabled.

       Termination=
           Takes a boolean or a termination resistor value in ohm in the range 0...65535. When
           "yes", the termination resistor is set to 120 ohm. When "no" or "0" is set, the
           termination resistor is disabled. When unset, the kernel's default will be used.

       TripleSampling=
           Takes a boolean. When "yes", three samples (instead of one) are used to determine the
           value of a received bit by majority rule. When unset, the kernel's default will be
           used.

       BusErrorReporting=
           Takes a boolean. When "yes", reporting of CAN bus errors is activated (those include
           single bit, frame format, and bit stuffing errors, unable to send dominant bit, unable
           to send recessive bit, bus overload, active error announcement, error occurred on
           transmission). When unset, the kernel's default will be used. Note: in case of a CAN
           bus with a single CAN device, sending a CAN frame may result in a huge number of CAN
           bus errors.

       ListenOnly=
           Takes a boolean. When "yes", listen-only mode is enabled. When the interface is in
           listen-only mode, the interface neither transmit CAN frames nor send ACK bit.
           Listen-only mode is important to debug CAN networks without interfering with the
           communication or acknowledge the CAN frame. When unset, the kernel's default will be
           used.

       Loopback=
           Takes a boolean. When "yes", loopback mode is enabled. When the loopback mode is
           enabled, the interface treats messages transmitted by itself as received messages. The
           loopback mode is important to debug CAN networks. When unset, the kernel's default
           will be used.

       OneShot=
           Takes a boolean. When "yes", one-shot mode is enabled. When unset, the kernel's
           default will be used.

       PresumeAck=
           Takes a boolean. When "yes", the interface will ignore missing CAN ACKs. When unset,
           the kernel's default will be used.

       ClassicDataLengthCode=
           Takes a boolean. When "yes", the interface will handle the 4bit data length code
           (DLC). When unset, the kernel's default will be used.

[IPOIB] SECTION OPTIONS

       The [IPoIB] section manages the IP over Infiniband and accepts the following keys:

       Mode=
           Takes one of the special values "datagram" or "connected". Defaults to unset, and the
           kernel's default is used.

           When "datagram", the Infiniband unreliable datagram (UD) transport is used, and so the
           interface MTU is equal to the IB L2 MTU minus the IPoIB encapsulation header (4
           bytes). For example, in a typical IB fabric with a 2K MTU, the IPoIB MTU will be 2048
           - 4 = 2044 bytes.

           When "connected", the Infiniband reliable connected (RC) transport is used. Connected
           mode takes advantage of the connected nature of the IB transport and allows an MTU up
           to the maximal IP packet size of 64K, which reduces the number of IP packets needed
           for handling large UDP datagrams, TCP segments, etc and increases the performance for
           large messages.

       IgnoreUserspaceMulticastGroup=
           Takes an boolean value. When true, the kernel ignores multicast groups handled by
           userspace. Defaults to unset, and the kernel's default is used.

[QDISC] SECTION OPTIONS

       The [QDisc] section manages the traffic control queueing discipline (qdisc).

       Parent=
           Specifies the parent Queueing Discipline (qdisc). Takes one of "clsact" or "ingress".
           This is mandatory.

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

[NETWORKEMULATOR] SECTION OPTIONS

       The [NetworkEmulator] section manages the queueing discipline (qdisc) of the network
       emulator. It can be used to configure the kernel packet scheduler and simulate packet
       delay and loss for UDP or TCP applications, or limit the bandwidth usage of a particular
       service to simulate internet connections.

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       DelaySec=
           Specifies the fixed amount of delay to be added to all packets going out of the
           interface. Defaults to unset.

       DelayJitterSec=
           Specifies the chosen delay to be added to the packets outgoing to the network
           interface. Defaults to unset.

       PacketLimit=
           Specifies the maximum number of packets the qdisc may hold queued at a time. An
           unsigned integer in the range 0...4294967294. Defaults to 1000.

       LossRate=
           Specifies an independent loss probability to be added to the packets outgoing from the
           network interface. Takes a percentage value, suffixed with "%". Defaults to unset.

       DuplicateRate=
           Specifies that the chosen percent of packets is duplicated before queuing them. Takes
           a percentage value, suffixed with "%". Defaults to unset.

[TOKENBUCKETFILTER] SECTION OPTIONS

       The [TokenBucketFilter] section manages the queueing discipline (qdisc) of token bucket
       filter (tbf).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       LatencySec=
           Specifies the latency parameter, which specifies the maximum amount of time a packet
           can sit in the Token Bucket Filter (TBF). Defaults to unset.

       LimitBytes=
           Takes the number of bytes that can be queued waiting for tokens to become available.
           When the size is suffixed with K, M, or G, it is parsed as Kilobytes, Megabytes, or
           Gigabytes, respectively, to the base of 1024. Defaults to unset.

       BurstBytes=
           Specifies the size of the bucket. This is the maximum amount of bytes that tokens can
           be available for instantaneous transfer. When the size is suffixed with K, M, or G, it
           is parsed as Kilobytes, Megabytes, or Gigabytes, respectively, to the base of 1024.
           Defaults to unset.

       Rate=
           Specifies the device specific bandwidth. When suffixed with K, M, or G, the specified
           bandwidth is parsed as Kilobits, Megabits, or Gigabits, respectively, to the base of
           1000. Defaults to unset.

       MPUBytes=
           The Minimum Packet Unit (MPU) determines the minimal token usage (specified in bytes)
           for a packet. When suffixed with K, M, or G, the specified size is parsed as
           Kilobytes, Megabytes, or Gigabytes, respectively, to the base of 1024. Defaults to
           zero.

       PeakRate=
           Takes the maximum depletion rate of the bucket. When suffixed with K, M, or G, the
           specified size is parsed as Kilobits, Megabits, or Gigabits, respectively, to the base
           of 1000. Defaults to unset.

       MTUBytes=
           Specifies the size of the peakrate bucket. When suffixed with K, M, or G, the
           specified size is parsed as Kilobytes, Megabytes, or Gigabytes, respectively, to the
           base of 1024. Defaults to unset.

[PIE] SECTION OPTIONS

       The [PIE] section manages the queueing discipline (qdisc) of Proportional Integral
       controller-Enhanced (PIE).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the queue size in number of packets. When this limit is
           reached, incoming packets are dropped. An unsigned integer in the range
           1...4294967294. Defaults to unset and kernel's default is used.

[FLOWQUEUEPIE] SECTION OPTIONS

       The "[FlowQueuePIE]" section manages the queueing discipline (qdisc) of Flow Queue
       Proportional Integral controller-Enhanced (fq_pie).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the queue size in number of packets. When this limit is
           reached, incoming packets are dropped. An unsigned integer ranges 1 to 4294967294.
           Defaults to unset and kernel's default is used.

[STOCHASTICFAIRBLUE] SECTION OPTIONS

       The [StochasticFairBlue] section manages the queueing discipline (qdisc) of stochastic
       fair blue (sfb).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the queue size in number of packets. When this limit is
           reached, incoming packets are dropped. An unsigned integer in the range
           0...4294967294. Defaults to unset and kernel's default is used.

[STOCHASTICFAIRNESSQUEUEING] SECTION OPTIONS

       The [StochasticFairnessQueueing] section manages the queueing discipline (qdisc) of
       stochastic fairness queueing (sfq).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PerturbPeriodSec=
           Specifies the interval in seconds for queue algorithm perturbation. Defaults to unset.

[BFIFO] SECTION OPTIONS

       The [BFIFO] section manages the queueing discipline (qdisc) of Byte limited Packet First
       In First Out (bfifo).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       LimitBytes=
           Specifies the hard limit in bytes on the FIFO buffer size. The size limit prevents
           overflow in case the kernel is unable to dequeue packets as quickly as it receives
           them. When this limit is reached, incoming packets are dropped. When suffixed with K,
           M, or G, the specified size is parsed as Kilobytes, Megabytes, or Gigabytes,
           respectively, to the base of 1024. Defaults to unset and kernel default is used.

[PFIFO] SECTION OPTIONS

       The [PFIFO] section manages the queueing discipline (qdisc) of Packet First In First Out
       (pfifo).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the number of packets in the FIFO queue. The size limit
           prevents overflow in case the kernel is unable to dequeue packets as quickly as it
           receives them. When this limit is reached, incoming packets are dropped. An unsigned
           integer in the range 0...4294967294. Defaults to unset and kernel's default is used.

[PFIFOHEADDROP] SECTION OPTIONS

       The [PFIFOHeadDrop] section manages the queueing discipline (qdisc) of Packet First In
       First Out Head Drop (pfifo_head_drop).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           As in [PFIFO] section.

[PFIFOFAST] SECTION OPTIONS

       The [PFIFOFast] section manages the queueing discipline (qdisc) of Packet First In First
       Out Fast (pfifo_fast).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

[CAKE] SECTION OPTIONS

       The [CAKE] section manages the queueing discipline (qdisc) of Common Applications Kept
       Enhanced (CAKE).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       Bandwidth=
           Specifies the shaper bandwidth. When suffixed with K, M, or G, the specified size is
           parsed as Kilobits, Megabits, or Gigabits, respectively, to the base of 1000. Defaults
           to unset and kernel's default is used.

       AutoRateIngress=
           Takes a boolean value. Enables automatic capacity estimation based on traffic arriving
           at this qdisc. This is most likely to be useful with cellular links, which tend to
           change quality randomly. If this setting is enabled, the Bandwidth= setting is used as
           an initial estimate. Defaults to unset, and the kernel's default is used.

       OverheadBytes=
           Specifies that bytes to be addeded to the size of each packet. Bytes may be negative.
           Takes an integer in the range -64...256. Defaults to unset and kernel's default is
           used.

       MPUBytes=
           Rounds each packet (including overhead) up to the specified bytes. Takes an integer in
           the range 1...256. Defaults to unset and kernel's default is used.

       CompensationMode=
           Takes one of "none", "atm", or "ptm". Specifies the compensation mode for overhead
           calculation. When "none", no compensation is taken into account. When "atm", enables
           the compensation for ATM cell framing, which is normally found on ADSL links. When
           "ptm", enables the compensation for PTM encoding, which is normally found on VDSL2
           links and uses a 64b/65b encoding scheme. Defaults to unset and the kernel's default
           is used.

       UseRawPacketSize=
           Takes a boolean value. When true, the packet size reported by the Linux kernel will be
           used, instead of the underlying IP packet size. Defaults to unset, and the kernel's
           default is used.

       FlowIsolationMode=
           CAKE places packets from different flows into different queues, then packets from each
           queue are delivered fairly. This specifies whether the fairness is based on source
           address, destination address, individual flows, or any combination of those. The
           available values are:

           none
               The flow isolation is disabled, and all traffic passes through a single queue.

           src-host
               Flows are defined only by source address. Equivalent to the "srchost" option for
               tc qdisc command. See also tc-cake(8).

           dst-host
               Flows are defined only by destination address. Equivalent to the "dsthost" option
               for tc qdisc command. See also tc-cake(8).

           hosts
               Flows are defined by source-destination host pairs. Equivalent to the same option
               for tc qdisc command. See also tc-cake(8).

           flows
               Flows are defined by the entire 5-tuple of source address, destination address,
               transport protocol, source port and destination port. Equivalent to the same
               option for tc qdisc command. See also tc-cake(8).

           dual-src-host
               Flows are defined by the 5-tuple (see "flows" in the above), and fairness is
               applied first over source addresses, then over individual flows. Equivalent to the
               "dual-srchost" option for tc qdisc command. See also tc-cake(8).

           dual-dst-host
               Flows are defined by the 5-tuple (see "flows" in the above), and fairness is
               applied first over destination addresses, then over individual flows. Equivalent
               to the "dual-dsthost" option for tc qdisc command. See also tc-cake(8).

           triple
               Flows are defined by the 5-tuple (see "flows"), and fairness is applied over
               source and destination addresses, and also over individual flows. Equivalent to
               the "triple-isolate" option for tc qdisc command. See also tc-cake(8).

           Defaults to unset and the kernel's default is used.

       NAT=
           Takes a boolean value. When true, CAKE performs a NAT lookup before applying
           flow-isolation rules, to determine the true addresses and port numbers of the packet,
           to improve fairness between hosts inside the NAT. This has no practical effect when
           FlowIsolationMode= is "none" or "flows", or if NAT is performed on a different host.
           Defaults to unset, and the kernel's default is used.

       PriorityQueueingPreset=
           CAKE divides traffic into "tins", and each tin has its own independent set of
           flow-isolation queues, bandwidth threshold, and priority. This specifies the preset of
           tin profiles. The available values are:

           besteffort
               Disables priority queueing by placing all traffic in one tin.

           precedence
               Enables priority queueing based on the legacy interpretation of TOS "Precedence"
               field. Use of this preset on the modern Internet is firmly discouraged.

           diffserv8
               Enables priority queueing based on the Differentiated Service ("DiffServ") field
               with eight tins: Background Traffic, High Throughput, Best Effort, Video
               Streaming, Low Latency Transactions, Interactive Shell, Minimum Latency, and
               Network Control.

           diffserv4
               Enables priority queueing based on the Differentiated Service ("DiffServ") field
               with four tins: Background Traffic, Best Effort, Streaming Media, and Latency
               Sensitive.

           diffserv3
               Enables priority queueing based on the Differentiated Service ("DiffServ") field
               with three tins: Background Traffic, Best Effort, and Latency Sensitive.

           Defaults to unset, and the kernel's default is used.

       FirewallMark=
           Takes an integer in the range 1...4294967295. When specified, firewall-mark-based
           overriding of CAKE's tin selection is enabled. Defaults to unset, and the kernel's
           default is used.

       Wash=
           Takes a boolean value. When true, CAKE clears the DSCP fields, except for ECN bits, of
           any packet passing through CAKE. Defaults to unset, and the kernel's default is used.

       SplitGSO=
           Takes a boolean value. When true, CAKE will split General Segmentation Offload (GSO)
           super-packets into their on-the-wire components and dequeue them individually.
           Defaults to unset, and the kernel's default is used.

       RTTSec=
           Specifies the RTT for the filter. Takes a timespan. Typical values are e.g. 100us for
           extremely high-performance 10GigE+ networks like datacentre, 1ms for non-WiFi LAN
           connections, 100ms for typical internet connections. Defaults to unset, and the
           kernel's default will be used.

       AckFilter=
           Takes a boolean value, or special value "aggressive". If enabled, ACKs in each flow
           are queued and redundant ACKs to the upstream are dropped. If yes, the filter will
           always keep at least two redundant ACKs in the queue, while in "aggressive" mode, it
           will filter down to a single ACK. This may improve download throughput on links with
           very asymmetrical rate limits. Defaults to unset, and the kernel's default will be
           used.

[CONTROLLEDDELAY] SECTION OPTIONS

       The [ControlledDelay] section manages the queueing discipline (qdisc) of controlled delay
       (CoDel).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the queue size in number of packets. When this limit is
           reached, incoming packets are dropped. An unsigned integer in the range
           0...4294967294. Defaults to unset and kernel's default is used.

       TargetSec=
           Takes a timespan. Specifies the acceptable minimum standing/persistent queue delay.
           Defaults to unset and kernel's default is used.

       IntervalSec=
           Takes a timespan. This is used to ensure that the measured minimum delay does not
           become too stale. Defaults to unset and kernel's default is used.

       ECN=
           Takes a boolean. This can be used to mark packets instead of dropping them. Defaults
           to unset and kernel's default is used.

       CEThresholdSec=
           Takes a timespan. This sets a threshold above which all packets are marked with ECN
           Congestion Experienced (CE). Defaults to unset and kernel's default is used.

[DEFICITROUNDROBINSCHEDULER] SECTION OPTIONS

       The [DeficitRoundRobinScheduler] section manages the queueing discipline (qdisc) of
       Deficit Round Robin Scheduler (DRR).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

[DEFICITROUNDROBINSCHEDULERCLASS] SECTION OPTIONS

       The [DeficitRoundRobinSchedulerClass] section manages the traffic control class of Deficit
       Round Robin Scheduler (DRR).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", or a qdisc
           identifier. The qdisc identifier is specified as the major and minor numbers in
           hexadecimal in the range 0x1–0xffff separated with a colon ("major:minor"). Defaults
           to "root".

       ClassId=
           Configures the unique identifier of the class. It is specified as the major and minor
           numbers in hexadecimal in the range 0x1–0xffff separated with a colon ("major:minor").
           Defaults to unset.

       QuantumBytes=
           Specifies the amount of bytes a flow is allowed to dequeue before the scheduler moves
           to the next class. When suffixed with K, M, or G, the specified size is parsed as
           Kilobytes, Megabytes, or Gigabytes, respectively, to the base of 1024. Defaults to the
           MTU of the interface.

[ENHANCEDTRANSMISSIONSELECTION] SECTION OPTIONS

       The [EnhancedTransmissionSelection] section manages the queueing discipline (qdisc) of
       Enhanced Transmission Selection (ETS).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       Bands=
           Specifies the number of bands. An unsigned integer in the range 1...16. This value has
           to be at least large enough to cover the strict bands specified through the
           StrictBands= and bandwidth-sharing bands specified in QuantumBytes=.

       StrictBands=
           Specifies the number of bands that should be created in strict mode. An unsigned
           integer in the range 1...16.

       QuantumBytes=
           Specifies the white-space separated list of quantum used in band-sharing bands. When
           suffixed with K, M, or G, the specified size is parsed as Kilobytes, Megabytes, or
           Gigabytes, respectively, to the base of 1024. This setting can be specified multiple
           times. If an empty string is assigned, then the all previous assignments are cleared.

       PriorityMap=
           The priority map maps the priority of a packet to a band. The argument is a whitespace
           separated list of numbers. The first number indicates which band the packets with
           priority 0 should be put to, the second is for priority 1, and so on. There can be up
           to 16 numbers in the list. If there are fewer, the default band that traffic with one
           of the unmentioned priorities goes to is the last one. Each band number must be in the
           range 0...255. This setting can be specified multiple times. If an empty string is
           assigned, then the all previous assignments are cleared.

[GENERICRANDOMEARLYDETECTION] SECTION OPTIONS

       The [GenericRandomEarlyDetection] section manages the queueing discipline (qdisc) of
       Generic Random Early Detection (GRED).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       VirtualQueues=
           Specifies the number of virtual queues. Takes an integer in the range 1...16. Defaults
           to unset and kernel's default is used.

       DefaultVirtualQueue=
           Specifies the number of default virtual queue. This must be less than VirtualQueue=.
           Defaults to unset and kernel's default is used.

       GenericRIO=
           Takes a boolean. It turns on the RIO-like buffering scheme. Defaults to unset and
           kernel's default is used.

[FAIRQUEUEINGCONTROLLEDDELAY] SECTION OPTIONS

       The [FairQueueingControlledDelay] section manages the queueing discipline (qdisc) of fair
       queuing controlled delay (FQ-CoDel).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the real queue size. When this limit is reached, incoming
           packets are dropped. Defaults to unset and kernel's default is used.

       MemoryLimitBytes=
           Specifies the limit on the total number of bytes that can be queued in this FQ-CoDel
           instance. When suffixed with K, M, or G, the specified size is parsed as Kilobytes,
           Megabytes, or Gigabytes, respectively, to the base of 1024. Defaults to unset and
           kernel's default is used.

       Flows=
           Specifies the number of flows into which the incoming packets are classified. Defaults
           to unset and kernel's default is used.

       TargetSec=
           Takes a timespan. Specifies the acceptable minimum standing/persistent queue delay.
           Defaults to unset and kernel's default is used.

       IntervalSec=
           Takes a timespan. This is used to ensure that the measured minimum delay does not
           become too stale. Defaults to unset and kernel's default is used.

       QuantumBytes=
           Specifies the number of bytes used as the "deficit" in the fair queuing algorithm
           timespan. When suffixed with K, M, or G, the specified size is parsed as Kilobytes,
           Megabytes, or Gigabytes, respectively, to the base of 1024. Defaults to unset and
           kernel's default is used.

       ECN=
           Takes a boolean. This can be used to mark packets instead of dropping them. Defaults
           to unset and kernel's default is used.

       CEThresholdSec=
           Takes a timespan. This sets a threshold above which all packets are marked with ECN
           Congestion Experienced (CE). Defaults to unset and kernel's default is used.

[FAIRQUEUEING] SECTION OPTIONS

       The [FairQueueing] section manages the queueing discipline (qdisc) of fair queue traffic
       policing (FQ).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the real queue size. When this limit is reached, incoming
           packets are dropped. Defaults to unset and kernel's default is used.

       FlowLimit=
           Specifies the hard limit on the maximum number of packets queued per flow. Defaults to
           unset and kernel's default is used.

       QuantumBytes=
           Specifies the credit per dequeue RR round, i.e. the amount of bytes a flow is allowed
           to dequeue at once. When suffixed with K, M, or G, the specified size is parsed as
           Kilobytes, Megabytes, or Gigabytes, respectively, to the base of 1024. Defaults to
           unset and kernel's default is used.

       InitialQuantumBytes=
           Specifies the initial sending rate credit, i.e. the amount of bytes a new flow is
           allowed to dequeue initially. When suffixed with K, M, or G, the specified size is
           parsed as Kilobytes, Megabytes, or Gigabytes, respectively, to the base of 1024.
           Defaults to unset and kernel's default is used.

       MaximumRate=
           Specifies the maximum sending rate of a flow. When suffixed with K, M, or G, the
           specified size is parsed as Kilobits, Megabits, or Gigabits, respectively, to the base
           of 1000. Defaults to unset and kernel's default is used.

       Buckets=
           Specifies the size of the hash table used for flow lookups. Defaults to unset and
           kernel's default is used.

       OrphanMask=
           Takes an unsigned integer. For packets not owned by a socket, fq is able to mask a
           part of hash and reduce number of buckets associated with the traffic. Defaults to
           unset and kernel's default is used.

       Pacing=
           Takes a boolean, and enables or disables flow pacing. Defaults to unset and kernel's
           default is used.

       CEThresholdSec=
           Takes a timespan. This sets a threshold above which all packets are marked with ECN
           Congestion Experienced (CE). Defaults to unset and kernel's default is used.

[TRIVIALLINKEQUALIZER] SECTION OPTIONS

       The [TrivialLinkEqualizer] section manages the queueing discipline (qdisc) of trivial link
       equalizer (teql).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       Id=
           Specifies the interface ID "N" of teql. Defaults to "0". Note that when teql is used,
           currently, the module sch_teql with max_equalizers=N+1 option must be loaded before
           systemd-networkd is started.

[HIERARCHYTOKENBUCKET] SECTION OPTIONS

       The [HierarchyTokenBucket] section manages the queueing discipline (qdisc) of hierarchy
       token bucket (htb).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       DefaultClass=
           Takes the minor id in hexadecimal of the default class. Unclassified traffic gets sent
           to the class. Defaults to unset.

       RateToQuantum=
           Takes an unsigned integer. The DRR quantums are calculated by dividing the value
           configured in Rate= by RateToQuantum=.

[HIERARCHYTOKENBUCKETCLASS] SECTION OPTIONS

       The [HierarchyTokenBucketClass] section manages the traffic control class of hierarchy
       token bucket (htb).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", or a qdisc
           identifier. The qdisc identifier is specified as the major and minor numbers in
           hexadecimal in the range 0x1–0xffff separated with a colon ("major:minor"). Defaults
           to "root".

       ClassId=
           Configures the unique identifier of the class. It is specified as the major and minor
           numbers in hexadecimal in the range 0x1–0xffff separated with a colon ("major:minor").
           Defaults to unset.

       Priority=
           Specifies the priority of the class. In the round-robin process, classes with the
           lowest priority field are tried for packets first.

       QuantumBytes=
           Specifies how many bytes to serve from leaf at once. When suffixed with K, M, or G,
           the specified size is parsed as Kilobytes, Megabytes, or Gigabytes, respectively, to
           the base of 1024.

       MTUBytes=
           Specifies the maximum packet size we create. When suffixed with K, M, or G, the
           specified size is parsed as Kilobytes, Megabytes, or Gigabytes, respectively, to the
           base of 1024.

       OverheadBytes=
           Takes an unsigned integer which specifies per-packet size overhead used in rate
           computations. When suffixed with K, M, or G, the specified size is parsed as
           Kilobytes, Megabytes, or Gigabytes, respectively, to the base of 1024.

       Rate=
           Specifies the maximum rate this class and all its children are guaranteed. When
           suffixed with K, M, or G, the specified size is parsed as Kilobits, Megabits, or
           Gigabits, respectively, to the base of 1000. This setting is mandatory.

       CeilRate=
           Specifies the maximum rate at which a class can send, if its parent has bandwidth to
           spare. When suffixed with K, M, or G, the specified size is parsed as Kilobits,
           Megabits, or Gigabits, respectively, to the base of 1000. When unset, the value
           specified with Rate= is used.

       BufferBytes=
           Specifies the maximum bytes burst which can be accumulated during idle period. When
           suffixed with K, M, or G, the specified size is parsed as Kilobytes, Megabytes, or
           Gigabytes, respectively, to the base of 1024.

       CeilBufferBytes=
           Specifies the maximum bytes burst for ceil which can be accumulated during idle
           period. When suffixed with K, M, or G, the specified size is parsed as Kilobytes,
           Megabytes, or Gigabytes, respectively, to the base of 1024.

[HEAVYHITTERFILTER] SECTION OPTIONS

       The [HeavyHitterFilter] section manages the queueing discipline (qdisc) of Heavy Hitter
       Filter (hhf).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

       PacketLimit=
           Specifies the hard limit on the queue size in number of packets. When this limit is
           reached, incoming packets are dropped. An unsigned integer in the range
           0...4294967294. Defaults to unset and kernel's default is used.

[QUICKFAIRQUEUEING] SECTION OPTIONS

       The [QuickFairQueueing] section manages the queueing discipline (qdisc) of Quick Fair
       Queueing (QFQ).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", "clsact",
           "ingress" or a class identifier. The class identifier is specified as the major and
           minor numbers in hexadecimal in the range 0x1–0xffff separated with a colon
           ("major:minor"). Defaults to "root".

       Handle=
           Configures the major number of unique identifier of the qdisc, known as the handle.
           Takes a hexadecimal number in the range 0x1–0xffff. Defaults to unset.

[QUICKFAIRQUEUEINGCLASS] SECTION OPTIONS

       The [QuickFairQueueingClass] section manages the traffic control class of Quick Fair
       Queueing (qfq).

       Parent=
           Configures the parent Queueing Discipline (qdisc). Takes one of "root", or a qdisc
           identifier. The qdisc identifier is specified as the major and minor numbers in
           hexadecimal in the range 0x1–0xffff separated with a colon ("major:minor"). Defaults
           to "root".

       ClassId=
           Configures the unique identifier of the class. It is specified as the major and minor
           numbers in hexadecimal in the range 0x1–0xffff separated with a colon ("major:minor").
           Defaults to unset.

       Weight=
           Specifies the weight of the class. Takes an integer in the range 1...1023. Defaults to
           unset in which case the kernel default is used.

       MaxPacketBytes=
           Specifies the maximum packet size in bytes for the class. When suffixed with K, M, or
           G, the specified size is parsed as Kilobytes, Megabytes, or Gigabytes, respectively,
           to the base of 1024. When unset, the kernel default is used.

[BRIDGEVLAN] SECTION OPTIONS

       The [BridgeVLAN] section manages the VLAN ID configuration of a bridge port and accepts
       the following keys. Specify several [BridgeVLAN] sections to configure several VLAN
       entries. The VLANFiltering= option has to be enabled, see the [Bridge] section in
       systemd.netdev(5).

       VLAN=
           The VLAN ID allowed on the port. This can be either a single ID or a range M-N. Takes
           an integer in the range 1...4094.

       EgressUntagged=
           The VLAN ID specified here will be used to untag frames on egress. Configuring
           EgressUntagged= implicates the use of VLAN= above and will enable the VLAN ID for
           ingress as well. This can be either a single ID or a range M-N.

       PVID=
           The Port VLAN ID specified here is assigned to all untagged frames at ingress.  PVID=
           can be used only once. Configuring PVID= implicates the use of VLAN= above and will
           enable the VLAN ID for ingress as well.

EXAMPLES

       Example 1. Static network configuration

           # /etc/systemd/network/50-static.network
           [Match]
           Name=enp2s0

           [Network]
           Address=192.168.0.15/24
           Gateway=192.168.0.1

       This brings interface "enp2s0" up with a static address. The specified gateway will be
       used for a default route.

       Example 2. DHCP on ethernet links

           # /etc/systemd/network/80-dhcp.network
           [Match]
           Name=en*

           [Network]
           DHCP=yes

       This will enable DHCPv4 and DHCPv6 on all interfaces with names starting with "en" (i.e.
       ethernet interfaces).

       Example 3. IPv6 Prefix Delegation (DHCPv6 PD)

           # /etc/systemd/network/55-dhcpv6-pd-upstream.network
           [Match]
           Name=enp1s0

           [Network]
           DHCP=ipv6

           # The below setting is optional, to also assign an address in the delegated prefix
           # to the upstream interface. If not necessary, then comment out the line below and
           # the [DHCPPrefixDelegation] section.
           DHCPPrefixDelegation=yes

           # If the upstream network provides Router Advertisement with Managed bit set,
           # then comment out the line below and WithoutRA= setting in the [DHCPv6] section.
           IPv6AcceptRA=no

           [DHCPv6]
           WithoutRA=solicit

           [DHCPPrefixDelegation]
           UplinkInterface=:self
           SubnetId=0
           Announce=no

           # /etc/systemd/network/55-dhcpv6-pd-downstream.network
           [Match]
           Name=enp2s0

           [Network]
           DHCPPrefixDelegation=yes
           IPv6SendRA=yes

           # It is expected that the host is acting as a router. So, usually it is not
           # necessary to receive Router Advertisement from other hosts in the downstream network.
           IPv6AcceptRA=no

           [DHCPPrefixDelegation]
           UplinkInterface=enp1s0
           SubnetId=1
           Announce=yes

       This will enable DHCPv6-PD on the interface enp1s0 as an upstream interface where the
       DHCPv6 client is running and enp2s0 as a downstream interface where the prefix is
       delegated to. The delegated prefixes are distributed by IPv6 Router Advertisement on the
       downstream network.

       Example 4. IPv6 Prefix Delegation (DHCPv4 6RD)

           # /etc/systemd/network/55-dhcpv4-6rd-upstream.network
           [Match]
           Name=enp1s0

           [Network]
           DHCP=ipv4

           # When DHCPv4-6RD is used, the upstream network does not support IPv6.
           # Hence, it is not necessary to wait for Router Advertisement, which is enabled by default.
           IPv6AcceptRA=no

           [DHCPv4]
           Use6RD=yes

           # /etc/systemd/network/55-dhcpv4-6rd-downstream.network
           [Match]
           Name=enp2s0

           [Network]
           DHCPPrefixDelegation=yes
           IPv6SendRA=yes

           # It is expected that the host is acting as a router. So, usually it is not
           # necessary to receive Router Advertisement from other hosts in the downstream network.
           IPv6AcceptRA=no

           [DHCPPrefixDelegation]
           UplinkInterface=enp1s0
           SubnetId=1
           Announce=yes

       This will enable DHCPv4-6RD on the interface enp1s0 as an upstream interface where the
       DHCPv4 client is running and enp2s0 as a downstream interface where the prefix is
       delegated to. The delegated prefixes are distributed by IPv6 Router Advertisement on the
       downstream network.

       Example 5. A bridge with two enslaved links

           # /etc/systemd/network/25-bridge-static.netdev
           [NetDev]
           Name=bridge0
           Kind=bridge

           # /etc/systemd/network/25-bridge-static.network
           [Match]
           Name=bridge0

           [Network]
           Address=192.168.0.15/24
           Gateway=192.168.0.1
           DNS=192.168.0.1

           # /etc/systemd/network/25-bridge-slave-interface-1.network
           [Match]
           Name=enp2s0

           [Network]
           Bridge=bridge0

           # /etc/systemd/network/25-bridge-slave-interface-2.network
           [Match]
           Name=wlp3s0

           [Network]
           Bridge=bridge0

       This creates a bridge and attaches devices "enp2s0" and "wlp3s0" to it. The bridge will
       have the specified static address and network assigned, and a default route via the
       specified gateway will be added. The specified DNS server will be added to the global list
       of DNS resolvers.

       Example 6. Bridge port with VLAN forwarding

           # /etc/systemd/network/25-bridge-slave-interface-1.network
           [Match]
           Name=enp2s0

           [Network]
           Bridge=bridge0

           [BridgeVLAN]
           VLAN=1-32
           PVID=42
           EgressUntagged=42

           [BridgeVLAN]
           VLAN=100-200

           [BridgeVLAN]
           EgressUntagged=300-400

       This overrides the configuration specified in the previous example for the interface
       "enp2s0", and enables VLAN on that bridge port. VLAN IDs 1-32, 42, 100-400 will be
       allowed. Packets tagged with VLAN IDs 42, 300-400 will be untagged when they leave on this
       interface. Untagged packets which arrive on this interface will be assigned VLAN ID 42.

       Example 7. Various tunnels

           /etc/systemd/network/25-tunnels.network
           [Match]
           Name=ens1

           [Network]
           Tunnel=ipip-tun
           Tunnel=sit-tun
           Tunnel=gre-tun
           Tunnel=vti-tun

           /etc/systemd/network/25-tunnel-ipip.netdev
           [NetDev]
           Name=ipip-tun
           Kind=ipip

           /etc/systemd/network/25-tunnel-sit.netdev
           [NetDev]
           Name=sit-tun
           Kind=sit

           /etc/systemd/network/25-tunnel-gre.netdev
           [NetDev]
           Name=gre-tun
           Kind=gre

           /etc/systemd/network/25-tunnel-vti.netdev
           [NetDev]
           Name=vti-tun
           Kind=vti

       This will bring interface "ens1" up and create an IPIP tunnel, a SIT tunnel, a GRE tunnel,
       and a VTI tunnel using it.

       Example 8. A bond device

           # /etc/systemd/network/30-bond1.network
           [Match]
           Name=bond1

           [Network]
           DHCP=ipv6

           # /etc/systemd/network/30-bond1.netdev
           [NetDev]
           Name=bond1
           Kind=bond

           # /etc/systemd/network/30-bond1-dev1.network
           [Match]
           MACAddress=52:54:00:e9:64:41

           [Network]
           Bond=bond1

           # /etc/systemd/network/30-bond1-dev2.network
           [Match]
           MACAddress=52:54:00:e9:64:42

           [Network]
           Bond=bond1

       This will create a bond device "bond1" and enslave the two devices with MAC addresses
       52:54:00:e9:64:41 and 52:54:00:e9:64:42 to it. IPv6 DHCP will be used to acquire an
       address.

       Example 9. Virtual Routing and Forwarding (VRF)

       Add the "bond1" interface to the VRF master interface "vrf1". This will redirect routes
       generated on this interface to be within the routing table defined during VRF creation.
       For kernels before 4.8 traffic won't be redirected towards the VRFs routing table unless
       specific ip-rules are added.

           # /etc/systemd/network/25-vrf.network
           [Match]
           Name=bond1

           [Network]
           VRF=vrf1

       Example 10. MacVTap

       This brings up a network interface "macvtap-test" and attaches it to "enp0s25".

           # /lib/systemd/network/25-macvtap.network
           [Match]
           Name=enp0s25

           [Network]
           MACVTAP=macvtap-test

       Example 11. A Xfrm interface with physical underlying device.

           # /etc/systemd/network/27-xfrm.netdev
           [NetDev]
           Name=xfrm0
           Kind=xfrm

           [Xfrm]
           InterfaceId=7

           # /etc/systemd/network/27-eth0.network
           [Match]
           Name=eth0

           [Network]
           Xfrm=xfrm0

       This creates a "xfrm0" interface and binds it to the "eth0" device. This allows hardware
       based ipsec offloading to the "eth0" nic. If offloading is not needed, xfrm interfaces can
       be assigned to the "lo" device.

SEE ALSO

       systemd(1), systemd-networkd.service(8), systemd.link(5), systemd.netdev(5), systemd-
       network-generator.service(8), systemd-resolved.service(8)

NOTES

        1. System and Service Credentials
           https://systemd.io/CREDENTIALS

        2. Link-Local Multicast Name Resolution
           https://tools.ietf.org/html/rfc4795

        3. Multicast DNS
           https://tools.ietf.org/html/rfc6762

        4. DNS-over-TLS
           https://tools.ietf.org/html/rfc7858

        5. DNSSEC
           https://tools.ietf.org/html/rfc4033

        6. IEEE 802.1AB-2016
           https://standards.ieee.org/findstds/standard/802.1AB-2016.html

        7. IP Sysctl
           https://docs.kernel.org/networking/ip-sysctl.html

        8. RFC 4941
           https://tools.ietf.org/html/rfc4941

        9. RFC 1027
           https://tools.ietf.org/html/rfc1027

       10. RFC 6275
           https://tools.ietf.org/html/rfc6275

       11. RFC 5227
           https://tools.ietf.org/html/rfc5227

       12. RFC 4862
           https://tools.ietf.org/html/rfc4862

       13. RFC 3041
           https://tools.ietf.org/html/rfc3041

       14. NetLabel
           https://docs.kernel.org/netlabel/index.html

       15. Linux Security Modules (LSMs)
           https://en.wikipedia.org/wiki/Linux_Security_Modules

       16. NetLabel Fallback Peer Labeling
           https://github.com/SELinuxProject/selinux-notebook/blob/main/src/network_support.md

       17. RFC 3484
           https://tools.ietf.org/html/rfc3484

       18. RFC 4191
           https://tools.ietf.org/html/rfc4191

       19. RFC 8520
           https://tools.ietf.org/html/rfc8520

       20. RFC 7844
           https://tools.ietf.org/html/rfc7844

       21. C-style escapes
           https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences

       22. RFC 5969
           https://tools.ietf.org/html/rfc5969

       23. RFC 3315
           https://tools.ietf.org/html/rfc3315#section-17.2.1

       24. RFC 8415
           https://www.rfc-editor.org/rfc/rfc8415.html#section-6.3

       25. RFC 4291
           https://tools.ietf.org/html/rfc4291#section-2.5.4

       26. RFC 7217
           https://tools.ietf.org/html/rfc7217

       27. RFC 2131
           https://www.rfc-editor.org/rfc/rfc2131.html

       28. RFC 2132
           https://www.rfc-editor.org/rfc/rfc2132.html

       29. RFC 1542
           https://tools.ietf.org/html/rfc1542

       30. RFC 4861
           https://tools.ietf.org/html/rfc4861