Sep 29, 2012
Assuming this is a commercial cisco router you just put the second interface in the subnet they assigned you or run DHCP on it. Depends on the ISP. That part of the configuration is the easy part.

The much larger question is how do you actually manage to use 2 ISP. The answer pretty much is you can't other than a primary and a backup. The key problem is they you have 2 different IP addresses and if your user traffic would use both you will confuse sites on the internet and they will view it as a attack because they would see session data coming from 2 different IP addresses. You would have to find a way to manually load balance this so some users always use one connection and other users always use the other.