Dual homed frame relay

[lane]

I have a customer with a router config that has a single Frame T1 with 2 PVC's. Each PVC (sub-int) has its own DLCI, but they both have the same IP Address. How is that possible? First, whenever something like that has been attempted, IOS refuses it for me, but this customer swears that the config actually functions like dual homed circuit. I have never heard of this. Anyone seen this before?

[thisisshanky]

So, does the main interface have an IP ? Can you paste the original configs ? IOS wont let you have the same subnet configured on two different interfaces as long as they are up/up.

[Richard Burts]

IOS will not allow the same subnet to appear on two LAN interfaces. But in fact IOS will allow the same subnet to appear on two point to point interfaces.

I am not sure that there is much impact from having the same address on two point to point interfaces. It would be pretty much the same as having two point to point interfaces both using ip unnumbered referencing the same source IP.

HTH

Rick

[carlosv]

Exactly, the main point here is the state of the subinterfaces. If it's down then you can have the same IP on another interface. Try to assign a repeated IP address on a shutdown interface and the router will take it.

The FR service your customer has (may have) it´s called "Shadow PVC" which it's always down until the FR switch detects the loss of the "live" PVC and turns on the dormant PVC, this secondary PVC may terminate on another router so you have efectively an alternate path in case the main one is lost. Of course this only works if the actual physical link to the customer site it's up.

Carlos