Provided by: systemd_237-3ubuntu10_amd64 bug

NAME

       systemd.network - Network configuration

SYNOPSIS

       network.network

DESCRIPTION

       Network setup is performed by systemd-networkd(8).

       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 directory
       /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 lexical order, regardless of the directories in which
       they live. However, files with identical filenames replace each other. Files in /etc have
       the highest priority, files in /run take precedence over files with the same name in /lib.
       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 parsed after the file itself
       is 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 netdev file wherever
       located. (Of course, since /run is temporary and /usr/lib is for vendors, it is unlikely
       drop-ins should be used in either of those places.)

       Note that an interface without any static IPv6 addresses configured, and neither DHCPv6
       nor IPv6LL enabled, shall be considered to have no IPv6 support. IPv6 will be
       automatically disabled for that interface by writing "1" to
       /proc/sys/net/ipv6/conf/ifname/disable_ipv6.

[MATCH] SECTION OPTIONS

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

       A network file is said to match a device if each of the entries in the "[Match]" section
       matches, or if the section is empty. The following keys are accepted:

       MACAddress=
           The hardware address of the interface (use full colon-delimited hexadecimal, e.g.,
           01:23:45:67:89:ab).

       Path=
           A whitespace-separated list of shell-style globs matching the persistent path, as
           exposed by the udev property "ID_PATH". If the list is prefixed with a "!", the test
           is inverted; i.e. it is true when "ID_PATH" does not match any item in the list.

       Driver=
           A whitespace-separated list of shell-style globs matching the driver currently bound
           to the device, as exposed by the udev property "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 the udev property "DEVTYPE". If the list is prefixed with a "!", the test is
           inverted.

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

       Host=
           Matches against the hostname or machine ID of the host. See "ConditionHost=" in
           systemd.unit(5) for details.

       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.

       KernelCommandLine=
           Checks whether a specific kernel command line option is set (or if prefixed with the
           exclamation mark unset). See "ConditionKernelCommandLine=" in systemd.unit(5) for
           details.

       KernelVersion=
           Checks whether the kernel version (as reported by uname -r) matches a certain
           expression (or if prefixed with the exclamation mark does not match it). See
           "ConditionKernelVersion=" in systemd.unit(5) for details.

       Architecture=
           Checks whether the system is running on a specific architecture. See
           "ConditionArchitecture=" in systemd.unit(5) for details.

[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=
           A boolean. Enables or disables the ARP (low-level Address Resolution Protocol) for
           this interface. Defaults to unset, which means that the kernel 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.

       Unmanaged=
           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.

       RequiredForOnline=
           A boolean. When "yes", the network is deemed required when determining whether the
           system is online when running "systemd-networkd-wait-online". When "no", the network
           is ignored when checking for online state. Defaults to "yes".

           The network will be brought up normally in all cases, 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=true".

[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 Advertisement, if that is
           enabled, regardless of this parameter. By enabling DHCPv6 support explicitly, the
           DHCPv6 client will be started 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 "[DHCP]" section below for further configuration options for the DHCP client
           support.

       DHCPServer=
           A boolean. Enables DHCPv4 server support. 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", or "ipv6".
           Defaults to "ipv6".

       IPv4LLRoute=
           A boolean. When true, sets up the route needed for non-IPv4LL hosts to communicate
           with IPv4LL-only hosts. Defaults to false.

       IPv6Token=
           An IPv6 address with the top 64 bits unset. When set, indicates the 64-bit interface
           part of SLAAC IPv6 addresses for this link. Note that the token is only ever used for
           SLAAC, and not for DHCPv6 addresses, even in the case DHCP is requested by router
           advertisement. By default, the token is autogenerated.

       LLMNR=
           A boolean or "resolve". When true, enables Link-Local Multicast Name Resolution[1] 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=
           A boolean or "resolve". When true, enables Multicast DNS[2] 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).

       DNSSEC=
           A boolean or "allow-downgrade". When true, enables DNSSEC[3] 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 false. 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 host name, 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-2009[4]. 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.

       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. 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 fc00::/7 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. This setting is read by systemd-
           resolved.service(8).

       Domains=
           A 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 host names (host names containing no dots) to become fully qualified
           domain names (FQDNs). If a single-label host name 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 host names 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.

       NTP=
           An NTP server address. 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 either a boolean argument, 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.txt[5] 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 a
           boolean argument. Implies IPForward=ipv4. Defaults to "no".

       IPv6PrivacyExtensions=
           Configures use of stateless temporary addresses that change over time (see RFC
           4941[6], 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=
           Enable or disable IPv6 Router Advertisement (RA) reception support for the interface.
           Takes a boolean parameter. If true, RAs are accepted; if false, RAs are ignored,
           independently of the local forwarding state. When not set, the kernel default is used,
           and RAs are accepted only when local forwarding is disabled for that interface. 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.

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

           Also see ip-sysctl.txt[5] 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.

       IPv6DuplicateAddressDetection=
           Configures the amount of IPv6 Duplicate Address Detection (DAD) probes to send.
           Defaults to unset.

       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.
           Defaults to unset.

       IPv4ProxyARP=
           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[7]. Defaults to unset.

       IPv6ProxyNDP=
           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. Defautls to unset.

       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 option
           implies IPv6ProxyNDP=true but has no effect if IPv6ProxyNDP has been set to false.
           Defaults to unset.

       IPv6PrefixDelegation=
           Whether to enable or disable Router Advertisement sending on a link. Allowed values
           are "static" which distributes prefixes as defined in the "[IPv6PrefixDelegation]" and
           any "[IPv6Prefix]" sections, "dhcpv6" which requests prefixes using a DHCPv6 client
           configured for another link and any values configured in the "[IPv6PrefixDelegation]"
           section while ignoring all static prefix configuration sections, "yes" which uses both
           static configuration and DHCPv6, and "false" which turns off IPv6 prefix delegation
           altogether. Defaults to "false". See the "[IPv6PrefixDelegation]" and the
           "[IPv6Prefix]" sections for more configuration options.

       Bridge=
           The name of the bridge to add the link to. See systemd.netdev(5).

       Bond=
           The name of the bond to add the link to. See systemd.netdev(5).

       VRF=
           The name of the VRF to add the link to. See systemd.netdev(5).

       VLAN=
           The name of a VLAN to create on the link. See systemd.netdev(5). This option may be
           specified more than once.

       MACVLAN=
           The name of a MACVLAN to create on the link. See systemd.netdev(5). This option may be
           specified more than once.

       VXLAN=
           The name of a VXLAN to create on the link. See systemd.netdev(5). This option may be
           specified more than once.

       Tunnel=
           The name of a Tunnel to create on the link. See systemd.netdev(5). This option may be
           specified more than once.

       ActiveSlave=
           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=
           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=
           A boolean. Allows networkd to configure a specific link even if it has no carrier.
           Defaults to false.

[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 key is mandatory.

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

       Broadcast=
           The broadcast address, which must be in the format described in inet_pton(3). This key
           only applies to IPv4 addresses. If it is not given, it is derived from the "Address"
           key.

       Label=
           An address label.

       PreferredLifetime=
           Allows the default "preferred lifetime" of the address to be overridden. Only three
           settings are accepted: "forever" or "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", "link" or "host" or an unsigned
           integer ranges 0 to 255. Defaults to "global".

       HomeAddress=
           Takes a boolean argument. Designates this address the "home address" as defined in RFC
           6275[8]. Supported only on IPv6. Defaults to false.

       DuplicateAddressDetection=
           Takes a boolean argument. Do not perform Duplicate Address Detection RFC 4862[9] when
           adding this address. Supported only on IPv6. Defaults to false.

       ManageTemporaryAddress=
           Takes a boolean argument. If true the kernel manage temporary addresses created from
           this one as template on behalf of Privacy Extensions RFC 3041[10]. 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 to use privacy
           extensions in a manually configured network, just like if stateless auto-configuration
           was active. Defaults to false.

       PrefixRoute=
           Takes a boolean argument. When adding or modifying an IPv6 address, the userspace
           application needs a way to suppress adding a prefix route. This is for example
           relevant together with IFA_F_MANAGERTEMPADDR, where userspace creates autoconf
           generated addresses, but depending on on-link, no route for the prefix should be
           added. Defaults to false.

       AutoJoin=
           Takes a boolean argument. 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 then 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".

[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[11]. Precedence is managed by userspace, and only
       the label itself is stored in the kernel

       Label=
           The label for the prefix (an unsigned integer) ranges 0 to 4294967294. 0xffffffff is
           reserved. This key is mandatory.

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

[ROUTINGPOLICYRULE] SECTION OPTIONS

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

       TypeOfService=
           Specifies the type of service to match a number between 0 to 255.

       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 between 1 and
           4294967295).

       Table=
           Specifies the routing table identifier to lookup if the rule selector matches. The
           table identifier for a route (a number between 1 and 4294967295).

       Priority=
           Specifies the priority of this rule.  Priority= is an unsigned integer. Higher number
           means lower priority, and rules get processed in order of increasing number.

       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.

[ROUTE] SECTION OPTIONS

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

       Gateway=
           As in the "[Network]" section.

       GatewayOnlink=
           The "GatewayOnlink" option tells the kernel that it does not have to check if the
           gateway is reachable directly by the current machine (i.e., the kernel does not need
           to check if the gateway is attached to the local network), so that we can insert the
           route in the kernel table without it being complained about. A boolean, 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 (an unsigned integer).

       IPv6Preference=
           Specifies the route preference as defined in RFC4191[12] 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 route, which can be "global", "link" or "host". Defaults to "global".

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

       Table=num
           The table identifier for the route (a number between 1 and 4294967295, or 0 to unset).
           The table can be retrieved using ip route show table num.

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

       Type=
           The Type identifier for special route types, which can be "unicast" route to a
           destination network address which describes the path to the destination, "blackhole"
           packets are discarded silently, "unreachable" packets are discarded and the ICMP
           message host unreachable is generated, "prohibit" packets are discarded and the ICMP
           message communication administratively prohibited is generated. 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 data bytes will be sent during the initial burst
           of data. Takes a size in bytes between 1 and 4294967295 (2^32 - 1). The usual suffixes
           K, M, G are supported and are understood to the base of 1024. Defaults to unset.

       InitialAdvertisedReceiveWindow=
           The TCP initial advertised receive window is the amount of receive data (in bytes)
           that can initally 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 size in bytes between 1 and 4294967295 (2^32 - 1). The
           usual suffixes K, M, G are supported and are understood to the base of 1024. Defaults
           to unset.

       QuickAck=
           Takes a boolean argument. When true enables TCP quick ack mode for the route. Defaults
           to unset.

[DHCP] SECTION OPTIONS

       The "[DHCP]" section configures the DHCPv4 and DHCP6 client, if it is enabled with the
       DHCP= setting described above:

       UseDNS=
           When true (the default), the DNS servers received from the DHCP server will be used
           and take precedence over any statically configured ones.

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

       UseNTP=
           When true (the default), the NTP servers received from the DHCP server will be used by
           systemd-timesyncd and take precedence over any statically configured ones.

       UseMTU=
           When true, the interface maximum transmission unit from the DHCP server will be used
           on the current link. Defaults to false.

       Anonymize=
           Takes a boolean argument. When true, the options sent to the DHCP server will follow
           the RFC 7844[13] (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)).

           Note that this configuration will overwrite others. In concrete, the following
           variables will be ignored: SendHostname=, ClientIdentifier=, UseRoutes=,
           SendHostname=, UseMTU=, VendorClassIdentifier=, UseTimezone=.

       SendHostname=
           When true (the default), the machine's hostname will be sent to the DHCP server.

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

       Hostname=
           Use this value for the hostname which is sent to the DHCP server, instead of machine's
           hostname.

       UseDomains=
           Takes a boolean argument, 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,
           similar 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, similar 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 host names, 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".

       UseTimezone=
           When true, the timezone received from the DHCP server will be set as timezone of the
           local system. Defaults to "no".

       CriticalConnection=
           When true, the connection will never be torn down even if the DHCP lease expires. This
           is contrary to the DHCP specification, but may be the best choice if, say, the root
           filesystem relies on this connection. Defaults to false.

       ClientIdentifier=
           The DHCPv4 client identifier to use. Either "mac" to use the MAC address of the link
           or "duid" (the default, see below) to use an RFC4361-compliant Client ID.

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

       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.

       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.

       RouteMetric=
           Set the routing metric for routes specified by the DHCP server.

       RouteTable=num
           The table identifier for DHCP routes (a number between 1 and 4294967295, or 0 to
           unset). The table can be retrieved using ip route show table num.

           When used in combination with VRF= the VRF's routing table is used unless this
           parameter is specified.

       ListenPort=
           Allow setting custom port for the DHCP client to listen on.

       RapidCommit=
           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 enabled by both the DHCPv6 client and the DHCPv6 server, the two-message exchange
           is used, rather than the default four-method exchange (solicit, advertise, request,
           and reply). The two-message exchange provides faster client configuration and is
           beneficial in environments in which networks are under a heavy load. See RFC 3315[14]
           for details. Defaults to true.

[IPV6ACCEPTRA] SECTION OPTIONS

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

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

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

       UseDomains=
           Takes a boolean argument, 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, similar 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, similar 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 host names, 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 (a number
           between 1 and 4294967295, or 0 to unset). The table can be retrieved using ip route
           show table num.

[DHCPSERVER] SECTION OPTIONS

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

       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.

       EmitDNS=, DNS=
           Configures whether the DHCP leases handed out to clients shall contain DNS server
           information. The EmitDNS= setting takes a boolean argument and defaults to "yes". The
           DNS servers to pass to clients may be configured with the DNS= option, which takes a
           list of IPv4 addresses. 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 or NTP server information at a later point. DNS server propagation does
           not take /etc/resolv.conf into account. 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.

       EmitNTP=, NTP=
           Similar to the EmitDNS= and DNS= settings described above, these settings configure
           whether and what NTP server information shall be emitted as part of the DHCP lease.
           The same syntax, propagation semantics and defaults apply as for EmitDNS= and DNS=.

       EmitRouter=
           Similar to the EmitDNS= setting described above, this setting configures whether the
           DHCP lease should contain the router option. The same syntax, propagation semantics
           and defaults apply as for EmitDNS=.

       EmitTimezone=, Timezone=
           Configures whether the DHCP leases handed out to clients shall contain timezone
           information. The EmitTimezone= setting takes a boolean argument and 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.

[IPV6PREFIXDELEGATION] SECTION OPTIONS

       The "[IPv6PrefixDelegation]" section contains settings for sending IPv6 Router
       Advertisements and whether to act as a router, if enabled via the IPv6PrefixDelegation=
       option described above. IPv6 network prefixes are defined with one or more "[IPv6Prefix]"
       sections.

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

       RouterLifetimeSec=
           Configures the IPv6 router lifetime in seconds. If set, this host also announces
           itself in Router Advertisements as an IPv6 router for the network link. Defaults to
           unset, which means the host is not acting as a router.

       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[12] for details. Defaults to "medium".

       EmitDNS=, DNS=
           DNS= specifies a list of recursive DNS server IPv6 addresses that distributed via
           Router Advertisement messages when EmitDNS= is true. 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 with the highest priority default route
           are 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 with the highest priority default
           route are 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=.

[IPV6PREFIX] SECTION OPTIONS

       One or more "[IPv6Prefix]" sections contain the IPv6 prefixes that are announced via
       Router Advertisements. See RFC 4861[15] for further details.

       AddressAutoconfiguration=, OnLink=
           Boolean values 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 604800 seconds (one week) and ValidLifetimeSec=
           defaults to 2592000 seconds (30 days).

[BRIDGE] SECTION OPTIONS

       The "[Bridge]" section accepts the following keys.

       UnicastFlood=
           A boolean. Controls whether the bridge should flood traffic for which an FDB entry is
           missing and the destination is unknown through this port. Defaults to on.

       HairPin=
           A boolean. Configures whether traffic may be sent back out of the port on which it was
           received. By default, this flag is false, and the bridge will not forward traffic back
           out of the receiving port.

       UseBPDU=
           A boolean. Configures whether STP Bridge Protocol Data Units will be processed by the
           bridge port. Defaults to yes.

       FastLeave=
           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. Defaults to off.

       AllowPortToBeRoot=
           A boolean. Configures whether a given port is allowed to become a root port. Only used
           when STP is enabled on the bridge. Defaults to on.

       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.

       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.

[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 "[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. VLAN
           IDs are valid from 1 to 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. A bridge with two enslaved links

           # /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 4.

           # /etc/systemd/network/20-bridge-slave-interface-vlan.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 5. 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 6. 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 7. 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 8. 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

SEE ALSO

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

NOTES

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

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

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

        4. IEEE 802.1AB-2009
           http://standards.ieee.org/getieee802/download/802.1AB-2009.pdf

        5. ip-sysctl.txt
           https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt

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

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

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

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

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

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

       12. RFC4191
           https://tools.ietf.org/html/rfc4191

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

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

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