2port ethernet TransPort21 as cable/dsl failover

Is it possible to use a WR21 with 2 ethernet port to provide failover from a cable/dsl Internet connection? I want the cable/dsl to be the primary Internet connection and the cellular to be the failover. I only have a few embedded devices on the LAN side.
I assume the WAN(cable/dsl) would be LAN-0 and the local network would be LAN-1?

Is there any app note or documentation that would help with setup?

Thanks

Here is the exact app note you are thinking of:
http://ftp1.digi.com/support/documentation/AN_41_Eth_Backup_to_WWAN.pdf

It is fairly “easy” to setup and this scenario is deployed quite frequently.

I’m having the same problem too. dsl modem and router could not communicate other. computer connected to the router IP bloğund are different and do not have access to the internet. please help