Ubuntu Manpage: /etc/network/interfaces - interface configuration database

NAME

       /etc/network/interfaces - interface configuration database

DESCRIPTION

       The /etc/network/interfaces file is used to specify how network interfaces are configured.
       The file is processed by ifquery(8), ifup(8) and ifdown(8) to introspect and change system
       state.

       In most cases, syntax from legacy implementations is supported as well, but that syntax is
       not discussed in detail here.

FILE SYNTAX

       The interface configuration database is composed of a series of stanzas.  Hash symbols
       designate comments, which are ignored by the system.

       A stanza is a collection of triples, where a triple is a key and value combination that is
       related to an object.  Triples which are not associated with an object are considered to
       be part of the root of the configuration tree.

       All keywords are case-sensitive and are expected to be lower-case.

       The following is a simple example of a stanza:

           auto eth0
           iface eth0
               address 203.0.113.2/24
               gateway 203.0.113.1

       This stanza defines an interface named eth0 which is configured with an address of
       203.0.113.2 and gateway of 203.0.113.1.

SUPPORTED KEYWORDS FOR UNASSOCIATED TRIPLES

       auto object
           Designates that object should be automatically configured by the system when
           appropriate.

       iface object
           Begins a new declaration for object.  Any child keyword associated with the
           declaration will be stored inside object.

       source filename
           Includes the file filename as configuration data.

       source-directory directory
           Includes the files in directory as configuration data.

       template object
           Begins a new declaration for object, like iface, except that object is defined as a
           template.

SUPPORTED KEYWORDS FOR OBJECT TRIPLES

Any keyword may be used inside an interface declaration block, but the system will only
respond to certain keywords by default:

address address
Associates an IPv4 or IPv6 address in CIDR notation with the parent interface. If an
IP address without a prefix length is given a given netmask attribute is used if
present. If neither a prefix length nor a netmask are given a /24 or /64 prefix length
is presumed for IPv4 / IPv6 as of compatibility reasons to classic ifupdown.

netmask netmask
Associates a fallback netmask with the parent interface for addresses which do not
have a CIDR length set. This option is for backwards compatibility and should not be
used in new deployments.

point-to-point address
Sets the given IPv4 address as the peer address on the interface. This setting only
takes effect for the IPv4 address familiy and only makes sense in combination with a
/32 netmask. For compatiblity with ifupdown and ifupdown2, pointopoint is an alias for
this parameter.

gateway address
Associates an IPv4 or IPv6 address with the parent interface for use as a default
route (gateway). This usually is given once for IPv4 and once for IPv6 (in a Dual-
Stack setup).

link-type link-type
Denotes the link-type of the interface. When set to dummy, the interface is created as
a virtual dummy interfaces. When set to veth the interface is created as virtual veth
interface (pair).

veth-peer-name peer-name
Denotes the name of the veth peer interfaces. If not set the kernel will name the veth
peer interface as vethN with N being an integer number.

alias alias
Sets the given alias on the interface.

requires interfaces...
Designates one or more required interfaces that must be brought up before
configuration of the parent interface. Interfaces associated with the parent are taken
down at the same time as the parent.

inherit object
Designates that the configured interface should inherit configuration data from
object. Normally object must be a template.

use executor
Designates that an executor should be used. See EXECUTORS section for more
information on executors.

pre-down command
Runs command before taking the interface down.

down command
Runs command when the interface is taken down.

post-down command
Runs command after taking the interface down.

pre-up command
Runs command before bringing the interface up.

up command
Runs command when the interface is brought up.

post-up command
Runs command after bringing the interface up.

Additional packages such as bonding, bridge, tunnel, vrf and vxlan add additional keywords
to this vocabulary.

EXECUTORS

       The use keyword designates that an executor should be used. This system is extendable by
       additional packages, but the most common executors are:

       batman
           The interface is a B.A.T.M.A.N. adv. mesh interface. Configuration of B.A.T.M.A.N.
           adv. interfaces requires the batctl untiliy to be installed.

       bond
           The interface is a bonded interface.  Configuration of bonded interfaces requires the
           bonding package to be installed.

       bridge
           The interface is an ethernet bridge.  Configuration of ethernet bridges requires the
           bridge package to be installed.

       dhcp
           Use a DHCP client to learn the IPv4 address of an interface.

       forward
           Configures forwarding settings on the interface.

       loopback
           Designates the interface as a loopback device.

       ppp
           Designates the interface as a PPP device.  Configuration of PPP interfaces require the
           ppp and probably the pppoe packages to be installed.

       tunnel
           The interface is a tunnel.  Configuration of tunnels requires the tunnel package to be
           installed on Alpine Linux.

       vrf
           The interface is a VRF.  Configuration of VRFs requires the vrf package to be
           installed.

       vxlan
           The interface is a Virtual Extensible LAN (VXLAN) tunnel endpoint.

       wifi
           The interface is a Wi-Fi (IEEE 802.11) client interface. Configuration of the WiFi
           client interface requires the wireless-tools package to be installed. The
           wpa_supplicant package must also be installed to connect to hotspots using WPA-based
           security.

       wireguard
           The interface is a Wireguard VPN tunnel endpoint.

       Check interfaces-<executor>(5) for further informaton about a given executor and available
       configuration parameters.

       If the auto_executor_selection ifupdown-ng.conf option is enabled, use statements will
       automatically be added for executors when their configuration statements are present in
       the interfaces file.

EXAMPLES

       Configure a bridge interface br0 with bond0 attached to it, which is a failover between
       eth0 and eth1.  This requires the bonding and bridge packages to be installed:

           auto br0
           iface br0
               use bridge
               requires bond0
               address 203.0.113.2/24
               gateway 203.0.113.1

           iface bond0
               use bond
               requires eth0 eth1
               bond-mode 802.3ad
               bond-xmit-hash-policy layer2+3

       Configure a network interface to use DHCP to learn its IPv4 address:

           auto eth0
           iface eth0
               use dhcp

AUTHORS

       Ariadne Conill <ariadne@dereferenced.org>
       Maximilian Wilhelm <max@sdn.clinic>

                                            2024-03-13                              interfaces(5)