This article will show how to "bond" two Ethernet connections together to create an auto failover interface.
Bonding
Install packages
First install the 2 packages needed to enable bonding.
#apt-get install ifenslave-2.6 ifenslave
Config file for Lenny
When you use Lenny, you have to modify /etc/network/interfaces only.
auto bond0 iface bond0 inet static address 10.31.1.5 netmask 255.255.255.0 network 10.31.1.0 gateway 10.31.1.254 slaves eth0 eth1 bond_mode active-backup bond_miimon 100 bond_downdelay 200 bond_updelay 200
For more detail, see /usr/share/doc/ifenslave-2.6/README.Debian.
Config files for Etch (and older versions)
There are a few config files that need to be edited. Change your /etc/network/interfaces to look like this. You will need to remove the listings associated with the bonded interfaces such as eth0 and eth1. Change the interfaces (ie: eth0; eth1) to match your needs as well as the IP address information
auto bond0 iface bond0 inet static address 10.31.1.5 netmask 255.255.255.0 network 10.31.1.0 gateway 10.31.1.254 up /sbin/ifenslave bond0 eth0 eth1 down /sbin/ifenslave -d bond0 eth0 eth1
Add the following lines to /etc/modprobe.d/arch/i386
alias bond0 bonding options bonding mode=1 miimon=100 downdelay=200 updelay=200
Last add this line to /etc/modules
bonding
and run
#update-modules
After this you will need to restart the network service or reboot the system.