Provided by: systemd_229-4ubuntu21.31_amd64

NAME

       systemd.network - Network configuration

SYNOPSIS

       network.network

DESCRIPTION

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

       Network files 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").

[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.

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 "DRIVER" of its parent device, or if that is not set the driver as
exposed by "ethtool -i" of the device itself.

Type=
A whitespace-separated list of shell-style globs matching the device type, as exposed by the udev
property "DEVTYPE".

Name=
A whitespace-separated list of shell-style globs matching the device name, as exposed by the udev
property "INTERFACE".

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.

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.

       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.

       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.

       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".

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
"IPv6AcceptRouterAdvertisements=".

Furthermore, note that by default the domain name specified through DHCP is not used for name
resolution. See option UseDomains= below.

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. By default, it 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 DNSEC 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=
A boolean. When true, enables LLDP link receive support.

BindCarrier=
A port or a list of ports. When set, controls the behavior of the current interface. When all ports
in the list are in an operational down state, the current interface is brought down. When at least
one port 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=
The domains used for DNS host name resolution on this link. Takes a list of DNS domain names which
are 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.

The specified domains are also used for routing of DNS queries: look-ups for host names ending in the
domains specified here are preferably routed to the DNS servers configured for this interface. If a
domain name is prefixed with "~", the domain name becomes a pure "routing" domain, is used for DNS
query routing purposes only and is not used in the described domain search logic. By specifying a
routing domain of "~." (the tilda indicating definition of a routing domain, the dot referring to
the DNS root domain which is the implied suffix of all valid DNS names) it is possible to route all
DNS traffic preferably to the DNS server specified for this interface. The route domain logic is
particularly useful on multi-homed hosts with DNS servers serving particular private DNS zones on
each interface.

This setting is read by systemd-resolved.service(8).

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[4] 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[5], 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".

IPv6AcceptRouterAdvertisements=
Force the setting of the accept_ra (router advertisements) setting for the interface. When unset, the
kernel default is used, and router advertisements are accepted only when local forwarding is disabled
for that interface. When router advertisements are accepted, they will trigger the start of the
DHCPv6 client if the relevant flags are passed, or if no routers are found on the link. Takes a
boolean. If true, router advertisements are accepted, when false, router advertisements are ignored,
independently of the local forwarding state.

See ip-sysctl.txt[4] in the kernel documentation, but note that systemd's setting of 1 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.

Bridge=
The name of the bridge to add the link to.

Bond=
The name of the bond to add the link to.

VLAN=
The name of a VLAN to create on the link. This option may be specified more than once.

MACVLAN=
The name of a MACVLAN to create on the link. This option may be specified more than once.

VXLAN=
The name of a VXLAN to create on the link. This option may be specified more than once.

Tunnel=
The name of a Tunnel to create on the link. This option may be specified more than once.

[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.

[ROUTE] SECTION OPTIONS

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

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

       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).

       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).

[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 true.

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 a 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 false.

It is recommended to enable this option only on trusted networks, as setting this affects resolution
of all host names, in particular to 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.

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=
DHCP client identifier to use. Either "mac" to use the MAC address of the link or "duid" (the
default) to use a RFC4361-compliant Client ID.

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

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.

[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=.

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.

[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 interger 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
interger 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 info is appended to the new
           static MAC table entry.

EXAMPLE

       Example 1. /etc/systemd/network/50-static.network

           [Match]
           Name=enp2s0

           [Network]
           Address=192.168.0.15/24
           Gateway=192.168.0.1

       Example 2. /etc/systemd/network/80-dhcp.network

           [Match]
           Name=en*

           [Network]
           DHCP=yes

       Example 3. /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

       Example 4. /etc/systemd/network/25-bridge-slave-interface.network

           [Match]
           Name=enp2s0

           [Network]
           Bridge=bridge0

       Example 5. /etc/systemd/network/25-ipip.network

           [Match]
           Name=em1

           [Network]
           Tunnel=ipip-tun

       Example 6. /etc/systemd/network/25-sit.network

           [Match]
           Name=em1

           [Network]
           Tunnel=sit-tun

       Example 7. /etc/systemd/network/25-gre.network

           [Match]
           Name=em1

           [Network]
           Tunnel=gre-tun

       Example 8. /etc/systemd/network/25-vti.network

           [Match]
           Name=em1

           [Network]
           Tunnel=vti-tun

       Example 9. /etc/systemd/network/25-bond.network

           [Match]
           Name=bond1

           [Network]
           DHCP=yes

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

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