5.3 KiB
ifupdown-ng for system administrators
ifupdown-ng is a network device manager which is backwards compatible with traditional ifup and ifdown as used on Debian and Alpine systems, while solving many design deficits with the original approach through robust error handling and the use of a dependency-solver to determine interface bring-up order.
This guide is intended to walk users through using the ifupdown-ng system without any assumption of familiarity with the legacy ifupdown system.
Important Filesystem Paths
The ifupdown-ng system uses the following paths, ranked in order of importance:
-
/etc/network/interfaces: the interface configuration database, which contains information about what interfaces should be configured. -
/run/ifstate: the interface state file, which denotes what physical interfaces are configured, and what interface definition they are configured as. -
/usr/libexec/ifupdown-ng: this directory contains the native ifupdown-ng executors, which are run as necessary to configure an interface. See the ifupdown-executor(7) manual page for more information on how these programs are written. -
/etc/network/if-{up|down|pre-up|post-down}.d: these directories contain scripts that are run when an interface is brought up or down. In general, they follow the same contract described in ifupdown-executor(7).
All configuration examples in this guide concern the
/etc/network/interfaces file.
Basic Configuration
To begin with, lets look at a basic configuration for a desktop computer. This scenario involves using the DHCP helper to learn an IPv4 address dynamically.
In this case, the /etc/network/interfaces file would
look like:
auto eth0
iface eth0
use dhcp
These configuration statements do two things: designate
that eth0 should be started automatically with the auto
keyword, and designate that the dhcp executor should be
used to configure the interface.
As a more detailed explanation, here is a commented version:
# Start eth0 automatically.
auto eth0
# Begin an interface definition for eth0.
iface eth0
# Use the dhcp executor to configure eth0.
use dhcp
IPv6 RA Configuration
With IPv6, stateless auto-configuration is typically used to
configure network interfaces. If you are not interested in
using IPv4 at all, you can simply use the ipv6-ra executor
to ensure that an interface is configured to accept IPv6 RA
advertisements:
auto eth0
iface eth0
use ipv6-ra
Static Configuration
We can use the static executor to configure static IPv4 and
IPv6 addresses. If you use the address keyword, the static
executor will automatically be used to configure the interface:
auto eth0
iface eth0
address 203.0.113.2/24
gateway 203.0.113.1
Multiple Addresses
A typical scenario on servers is where a server has multiple
IP addresses on a single interface. In this case you simply
add additional address lines like this:
auto eth0
iface eth0
address 203.0.113.2/24
address 203.0.113.3/24
address 203.0.113.4/24
gateway 203.0.113.1
Dual-stack configurations
Another typical scenario for servers is to run a dual-stack configuration, where interfaces have both an IPv4 and an IPv6 address. This is accomplished in a similar way as multi-homing. You specify the IPv4 and IPv6 addresses you want, followed by gateways for each:
auto eth0
iface eth0
address 203.0.113.2/24
address 203.0.113.3/24
address 203.0.113.4/24
gateway 203.0.113.1
address 2001:db8:1000:2::2/64
address 2001:db8:1000:2::3/64
address 2001:db8:1000:2::4/64
gateway 2001:db8:1000:2::1
Relationships
As previously mentioned, ifupdown-ng features a dependency resolver that allows for determining the interface configuration order.
In order to make use of this, dependencies can be managed in one of two ways:
Explicit dependency management using requires
The requires keyword can be used to manage explicit
dependencies:
auto eth0
iface eth0
use dhcp
auto gre0
iface gre0
requires eth0
use gre
gre-endpoint 203.0.113.2
gre-ttl 255
gre-flags ignore-df
address 203.0.113.194/30
gateway 203.0.113.193
Implicit dependency management using executors
Executors can declare implicit dependencies which work the same way as explicit dependencies, but are learned at run-time, for example:
auto bond0
iface bond0
use bond
bond-members eth0 eth1
[...]
Is equivalent to:
auto bond0
iface bond0
use bond
requires eth0 eth1
[...]
Executors
The ifupdown-ng system is expanded with additional features via
executors. Executors are selected on a per-interface basis using
use statements, for example:
auto eth0
iface eth0
use dhcp
Executors are run in the order specified by the use statements.
Some executors are automatically added based on other statements
in an interface definition. To see the full list of executors
used for an interface, use the ifquery(8) command.
Questions
If you have further questions about how to use ifupdown-ng to configure a specific scenario, drop by the ifupdown-ng IRC channel.