Cisco 2811 with HWIC-4ESW

I have a Cisco 2811 running IOS adventerprisek9-mz.12.4-15.T and a HWIC-4ESW installed.

Does anyone have the foggiest idea of how to get fa0/0 to share a vlan with fa0/0/0-3 (the ports on the HWIC-4ESW).

Any config files, urls, etc would be greatly appreciated.

Appendix D of the Cisco Field Manual: Catalyst Sw. Config covers "Extending VLANs within Layer 3 switches" and seems to be close but it shows a 802.1Q trunk line from the layer3 device to the layer 2 device--How's it handled when it is in the same box?


Doug Dougs@(8888nospam!!!!)

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Houston SBC
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Can't do it, since the built-in port is layer 3 only, and is not capable of running in layer 2 mode. It can only route traffic for vlan's but not act as an access port to a vlan.

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Actually, I did this just yesterday with a 2811 and the 9-port switch module. I eventually tore it back down again because it ate up cpu and it wasn't all that essential for me to have the other interface.

What you have to do is turn on bridging. Then you create a bridge virtual interface for the router to use instead of the vlan interface that connects to the switch module. Join both the vlan interface from the switch and the physical interface from the ouside of the router into the bridge group, and they're together.

bridge irb int fa0/0 no ip address bridge-group 1 int bvi 1 ip address x.x.x.x y.y.y.y int vlan 3 bridge-group 1 int fa0/0/2 switchport access vlan 3 bridge 1 protocol ieee bridge 1 route ip

What I did was similar, except that I was making my fa0/0 into a trunk to reach external switches, so each dot1q subinterface under it was linked to a separate bridge group. The 9-port module was then configured with one vlan for data and the other for voice to support ip phones. When I had it working, however, it chewed up 10-30% cpu with almost no traffic load. Shut down fa0/0, got rid of the bvi's and made the 9th port on the module into a trunk instead, and cpu ran about 1-2%, so that's where I'm leaving it. My guess would be that the bvi's are implemented in software, so don't optimize as well. Of course, your situation may require you to use the other ports, so go ahead & try it.

I haven't messed with bridging on routers all that much, so it's also possible that I missed something--the cpu hit may be avoided by application of slightly cleverer code...

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Mike Dorn

First, thanks for the info. Cisco docs are somewhat lacking in certain areas. It is always nice to see someone else going where no one else has gone before.


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