Provided by: ifupdown-multi_0.1.1_all 
NAME
ifupdown-multi-interfaces - ifupdown-multi extension for the interfaces(5) file format
DESCRIPTION
/etc/network/interfaces contains network interface information for the ifup(8) and
ifdown(8) commands. This manpage describes the ifupdown-multi extensions to the the
standard interfaces(5) file format.
The ifupdown-multi extensions to ifupdown integrate Linux's policy routing based support
for multiple default gateways on independent network connections. These extensions can
replace a typical shell script based approach that directly invokes a sequence of ip(8)
commands for configuring multiple uplinks with declarative syntax in the
/etc/network/interfaces file.
ifupdown-multi records the policy information used to bring up each network interface when
ifup(8) is run and removes the same policy routing information when ifdown(8) is run.
IFACE OPTIONS
The standard address and netmask options must be set for each interface. The gateway
option must NOT be set.
The new multi_gateway and multi_table options must be set to configure policy routing with
ifupdown-multi.
Additionally, the multi_gateway_weight and multi_preferred_prefixes options can be
specified in order to control optional policy routing features.
multi_gateway address
Default gateway for this interface. (Required.)
multi_table id
Table identifier. This must be a numeric value, and each interface must have a
unique value. Recommended range: 1-1000. (Required.)
multi_gateway_weight weight
Set this gateway's weight. This value is directly passed as the weight parameter to
the nexthop part of an ip-route(8) route object. Higher values indicate higher
relative bandwidth or quality. (Optional.)
multi_preferred_prefixes prefix [prefix]...
Prefer this connection for the given prefixes. This option configures the routing
policy database using the ip-rule(8) command to use this connection for the
specified prefixes. (Optional.)
EXAMPLES
The following example shows a basic configuration with two network interfaces. eth0 is on
the 198.51.100.0/24 network, while eth1 is on the 203.0.113.0/24 network. Each interface
stanza has a "multi_gateway" option, as opposed to the usual "gateway" option. Each
interface stanza also needs a "multi_table" option, whose parameter is a small, unique
non-negative integer. (This number will be used internally to uniquely identify an
interface-specific routing table.)
auto eth0
iface eth0 inet static
address 198.51.100.123
netmask 255.255.255.0
multi_table 1
multi_gateway 198.51.100.1
auto eth1
iface eth1 inet static
address 203.0.113.234
netmask 255.255.255.0
multi_table 2
multi_gateway 203.0.113.1
The following example shows a more complicated setup using optional ifupdown-multi
parameters. It is similar to the first example, but the network connection on eth0 is
preferred for most connections, and several network prefixes prefer to use one or the
other network connection.
auto eth0
iface eth0 inet static
address 198.51.100.123
netmask 255.255.255.0
multi_table 1
multi_gateway 198.51.100.1
multi_gateway_weight 5
multi_preferred_prefixes 10.0.0.0/8
auto eth1
iface eth1 inet static
address 203.0.113.234
netmask 255.255.255.0
multi_table 2
multi_gateway 203.0.113.1
multi_gateway_weight 1
multi_preferred_prefixes 172.16.0.0/12 192.168.0.0/16
FILES
/etc/network/interfaces
System-wide network interface configuration. See interfaces(5).
/var/run/network/ifupdown-multi.*
State information used by ifupdown-multi.
SEE ALSO
interfaces(5), ifup(8), ip(8), ip-route(8), ip-rule(8).
Linux Advanced Routing & Traffic Control HOWTO -- Chapter 4: Rules.
http://www.tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.rpdb.html