Cannot get bridging to work without creating a BVI interface

[Mohammed El-Batniji]

Dear freinds,

I need a help understanding why brigding between 2 interfaces on a router does not work until I create a BVI interface. Briefly, my setup is as follows:

I have a 6506 core switch connected to a 3845 router with 2 GigaEthernet interfaces. One of these interfaces is connected to the switch and the other connected to the ISP (WAN interface).

Due to some requirements, the ISP has extended a VLAN from a remote site to my WAN interface. My part involves extending this VLAN to the switch through the router. For that I configured IRB on the router to bridge traffic between both interfaces and finaly to the switch. I am wondering why this configuration does not work untill the BVI interface is created and configured with an IP address. I have a /30 subnet assigned for this setup and I am hoping to find a workaround instead of having to choose a bigger subnet to accomodate the BVI interface. I appreciate your help. 

[mlund]

Hi

When You configure bridging the router will, by default, only bridge those protocol that is not routed. Because ip is routed by default, ip packet's will not be bridged.

So You have two options here.

1. turn of ip routing .

2. configure an bvi

If You use the bvi, and will use the /30, try to set an fake address on the bvi.

/Mikael