[c-nsp] Bridging Serial Interfaces

[Todd Shipway]

I've got a rather basic question, or at least I hope it is.

A customer is trying to migrate from a point-to-point setup to a point-to-multipoint setup.  I'm trying to help them with this by supplying serial and multilink ppp interfaces.  They want these interfaces to be bridged.  I've got the interfaces up and running and when configured for routing, they work fine.  But they have strange default routing policies and need the bridging to be in place.  I setup the bridge-group on each of the interfaces and set the protocol to ieee.

interface Serial9/0/0/27:0
 no ip address
 no cdp enable
 bridge-group 2
!
interface Serial9/0/0/28:0
 no ip address
 no cdp enable
 bridge-group 2
bridge 2 protocol ieee
I show the bridge group to be up and running as expected:
Bridge Group 2 is running the IEEE compatible Spanning Tree protocol
   Port 106 (Serial9/0/0/27:0) of bridge group 2 is forwarding
   Port 107 (Serial9/0/0/28:0) of bridge group 2 is forwarding
 
The routers at the remote end of the serial links are configured as below....

Router1:
Interface serial 0
Ip address 172.16.0.1 255.255.255.252
Router2:
Interface serial 0
Ip address 172.16.0.2 255.255.255.252
Both router1 and router2 are using the default route below:
Ip route 0.0.0.0 0.0.0.0 serial 0

The issue is that no traffic will pass over the bridge.  Router1 is unable to ping router2 and vice versa.  Any ideas as to what I'm missing with this?
 
Thanks,
Todd