INTERFACES(5)

NAME
interfaces - network interface configuration for ifupdown

DESCRIPTION
By default, ifupdown2.conf sets /etc/network/interfaces as the network interface configuration file. This file contains information for the ifup(8), ifdown(8) and ifquery(8) commands.

This is where you configure how your system is connected to the network.

Lines starting with # are ignored. Note that end-of-line comments are NOT supported, comments must be on a line of their own.

A line may be extended across multiple lines by making the last character a backslash.

The file consists of zero or more "iface", "auto", "allow-" and "source" stanzas. Here is an example:

    auto lo eth0
    allow-hotplug eth1
    iface lo inet loopback
    source /etc/network/interfaces.d/bridges
    iface eth0 inet static
        address 192.168.1.1/24
        up flush-mail
    iface eth1 inet dhcp

Lines beginning with the word "auto" are used to identify the physical interfaces to be brought up when ifup is run with the -a option. (This option is used by the system boot scripts.) Physical interface names should follow the word "auto" on the same line. There can be multiple "auto" stanzas.

Lines beginning with "allow-" are used to identify interfaces that should be brought up automatically by various subsystems. This may be done using a command such as "ifup --allow=hotplug eth0 eth1", which will only bring up eth0 or eth1 if it is listed in an "allow-hotplug" line. Note that "allow-auto" and "auto" are synonyms.

Lines beginning with "source" are used to include stanzas from other files, so configuration can be split into many files. The word "source" is followed by the path of the file to be sourced. Shell wildcards can be used. Currently only supports absolute path names.

iface is normally given a interface name as its first non-option argument.

The interface name is followed by the name of the address family that the interface uses. This will be "inet" for TCP/IP networking and inet6 for ipv6. Following that is the name of the method used to configure the interface.

ifupdown supports iface stanzas without a family or a method. This enables using the same stanza for inet and inet6 family addresses. And the method defaults to "static"

Additional interface options/attributes can be given on subsequent lines in the iface stanza. These options come from addon modules. see ifupdown-addons-interfaces(5) for these options.

example bridge interface with additional attributes listed in the ifupdown-addons-interfaces(5) man page:

    auto br0
    iface br0
        address 12.0.0.4/24
        address 2000:1000:1000:1000:3::5/128
        bridge-ports swp1 swp2 swp3
        bridge-stp on

ifupdown supports python-mako style templates in the interfaces file. See examples section for details.

See /usr/share/doc/ifupdown2/examples/ for interfaces(5) file examples and interfaces file generation scripts.

METHODS
Both inet and inet6 address family interfaces can use the following methods (However they are not required):

The loopback Method
    This method may be used to define the loopback interface.

The static Method
    This method may be used to define ethernet interfaces with statically allocated addresses.

The dhcp Method
    This method may be used to obtain an address via DHCP.

BUILTIN INTERFACES
iface sections for some interfaces like physical interfaces or vlan interfaces in dot notation (like eth1.100) are understood by ifupdown. These interfaces do not need an entry in the interfaces file if they are dependents of other interfaces and don't need any specific configurations like addresses etc.

EXAMPLES
Sample /etc/network/interfaces file:

    auto lo
    iface lo
        address 192.168.2.0/24
        address 2001:dee:eeee:1::4/128
    auto eth0
    iface eth0 inet dhcp
    auto eth1
    iface eth1 inet manual
        address 192.168.2.0/24
        address 2001:dee:eeee:1::4/128
    # source files from a directory /etc/network/interfaces.d
    source /etc/network/interfaces.d/*
    # Using mako style templates
    % for v in [11,12]:
        auto vlan${v}
        iface vlan${v} inet static
            address 10.20.${v}.3/24
    % endfor

For additional syntax and examples see ifupdown-addons-interfaces(5)

FILES
configuration file defined in ifupdown2.conf (default /etc/network/interfaces)

SEE ALSO
ifupdown-addons-interfaces(5), ifup(8), ifquery(8), ifreload(8)

AUTHOR
Roopa Prabhu <roopa@cumulusnetworks.com>

COPYRIGHT
Copyright 2014 Cumulus Networks, Inc. All rights reserved.