Everybody wants redundancy. It's important to keep a server online even if a network card, switch or a cable fails.
If you're on CentOS, it's pretty easy to configure a redundant network connection for the server. The common approach to this problem is 'Interface bonding'. There are multiple operational modes for interface bonding, but I'll show only what you need to configure so the second connection is in stand-by until the main connection fails.
The steps you need to take:
Enable bonding module loading
You need to modify /etc/modprobe.conf, so the bonding module will be loaded by ifup scripts
If you 'forget' to create this file, you'll get an error message similar to the following:
Define the bonding interface in /etc/sysconfig/network-scripts
Yo uneed to create at least one file for the bonding interface: /etc/sysconfig/network-scripts/ifcfg-bond0, with a contents similar to the following:
Of course, if you have a different setup, you may enable DHCP and/or different bonding module options here
Configure the bonding slaves (the physical interfaces)
For each physical interface which will be 'bond'-ed, you need to create (or modify) a /etc/sysconfig/network-scripts/ifcfg-ethX file, with a contents similar to:
After all the mentioned configuration, the redundant configuration can be brought online by the command: