etcnetworkinterfaces

The /etc/network/interfaces file, commonly referred to as the interfaces file, is a traditional configuration mechanism for the ifupdown network management system used on Debian and many derivatives. It defines how network interfaces are configured at boot and when brought up or down, covering both IPv4 and IPv6 settings.

The file resides at /etc/network/interfaces and may reference additional per-interface definitions via source directives, such as source /etc/network/interfaces.d/* or source-directory /etc/network/interfaces.d. This modular approach allows grouping interface configurations across multiple files while still being managed by a single system component.

Configuration in the interfaces file is organized into stanzas for each interface. Each stanza starts with auto <iface> or allow-hotplug <iface>, followed by iface <iface> inet <method> for IPv4 or iface <iface> inet6 <method> for IPv6. The common methods are dhcp, static, and loopback. A minimal loopback entry is usually required:

auto lo

iface lo inet loopback

A typical Ethernet example using DHCP is:

auto eth0

iface eth0 inet dhcp

For a static IPv4 setup:

auto eth0

iface eth0 inet static

address 192.168.1.100

netmask 255.255.255.0

gateway 192.168.1.1

dns-nameservers 8.8.8.8 8.8.4.4

Usage and interaction: The system uses ifup to bring interfaces up and ifdown to take them down, and the networking service can be restarted with systemctl restart networking (or the equivalent SysV script on older systems). Modern distributions may employ alternative managers such as NetworkManager or systemd-networkd that can coexist or supersede ifupdown depending on configuration.

See also: ifupdown, /etc/network/interfaces, /etc/network/interfaces.d, network-manager, systemd-networkd.