John Patrick Lopez Tue, 06/05/2007 - 23:18

Just a follow up. I can see spanning-tree commands on a 3800 and 3700 router but not on a 2600 router.

Richard Burts Wed, 06/06/2007 - 06:01


I do not know the authoritative answer to your question about STP and BVI interface. But it seems to me that since the BVI does layer 2 to layer 3 or layer 3 to layer 2 forwarding but not layer 2 to layer 2 forwarding, that STP would not be involved with the BVI interface.



John Patrick Lopez Thu, 06/07/2007 - 02:45

I'm thinking about the two ports that will be performing the layer 2 switching and I'm thinking if it might cause loop. I'm planning to use BVI interface for internet router redundancy. Use two FastEthernet ports as a layer 2 ports and being member of the BVI interface and use the BVI interface as the gateway. This way I can connect one FastEthernet port to one core switch and the other to the other core to provide redundancy. Is this applicable?

Paolo Bevilacqua Thu, 06/07/2007 - 03:13

Yes, this is the usual method to connect a router with two Ethernet ports to two separate switches, still using a single subnet / IP address.

It works, but personally I never felt compelled to do that, because the failure rate of a switch is very very low, and often something better can be done with the 2nd ethernet port.

Hope this helps, please rate post if it does!

John Patrick Lopez Thu, 06/07/2007 - 03:41

Wow great! Now I know my idea will work. We just want to do this because sometimes, when we need to upgrade or if there's a problem with the first core then we can just reboot it without transfering the network connection to the second core. Thanks.

Paolo Bevilacqua Thu, 06/07/2007 - 04:06

Sure. Both interfaces have no ip address and are in the same bridge-group. IP address is put on the BVI. One interface will become blocked by SPT but will revert to the other as necessary. This works for both untagged or trunk interfaces so in fact you can have multiple subnets.

Thanks for the nice rating and good luck!


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