backup interface

[eric.cote]

I have read confusing reports that when using the command "backup interface" on a primary serial interface, the backup interface does not become active unless the primary interface experiences a loss of signal (layer-1). If only line protocol (layer-2) is down the back up link won't become active.

But, when I have been testing my potential config, backup interface command seems to work with only line protocal being down.

Can anyone confirm this?

[svermill]

A transition to protocol down has always been good enough in my experience.

[tepatel]

"Line protocol down" is good enaough to bring the backup interface out of standby mode..Backup interface will become active once line protocol will change the state to "down"..Thx..Tejal

[tim-griffin]

The problem shows up when using frame relay. If the PVC goes down, but the link to the frame switch is still up, traffic will continue to route over the frame relay path instead of the backup link path. I found that dialer-watch works much better in a frame relay environment with dial backup, but needs a routing protocol to trigger the dial backup.