Backing up a PVC with....ANOTHER PVC?

[IllegalOperation]

Hello,

We have a hub and spoke frame relay network. All routing is static. Each remote end has one physical circuit installed.

Our frame relay provider has it set up so each circuit has TWO DLCIs. One PVC is currently going back to the "hub", or the main distribution router. The other PVC will be used for fail-over purposes, as it is being routed down to our disaster recovery center.


My question is this:

I was ordered to incorporate the "disaster recovery" PVCs into operation by using the backup interface feature. In theory, the backup interface command fits our needs perfectly. We want it set up so that the backup interface will kick in after a long delay of the primary PVC going down.

However, we only have one physical circuit going to the Z (remote) ends of our network. Our routers only have one serial interface, so we will be using subinterfaces for each PVC.

Can you use the backup interface feature on subinterfaces (from the SAME physical interface)? It is my understanding that the physical interface itself needs to go down in order to trigger the backup interface. How is that possible with subinterfaces on a frame relay network?



For example...

s0.1 Main PVC (up/up)
s0.2 Disaster Recovery PVC (up/up)

If ONLY the s0.1 PVC goes down, interface serial0 itself will still be up. The backup interface will not kick in. Right? Or am I missing something?

 

[jneiberger]

The backup interface idea won't work at all. You need to do this by routing. Use floating static routes at your remote sites. You'll end up with a primary route pointing down the primary PVC and secondary route pointing down the secondary PVC.

The backup interface feature is for dial-on-demand routing, not for what you're trying to accomplish.