<root
SYSTEMD.NETWORK(5)                       systemd.network                       SYSTEMD.NETWORK(5)

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.

[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 false.

       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.

[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

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/rfc4795

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

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

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

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

systemd 229                                                                    SYSTEMD.NETWORK(5)

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