Unanswered Question
May 29th, 2009

Hi, I have one L2 switch having two vlan 4 & 5. I want communication between host of both vlans. How it can possible? Although I have configured Vlan-Bridge, but it is not working

interface Vlan4

bridge-group 1


interface Vlan5

bridge-group 1


bridge 1 protocol vlan-bridge

I have this problem too.
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Giuseppe Larosa Sat, 05/30/2009 - 08:26

Hello Rupesh,

vlan bridging can help if users on vlan4 and vlan5 are in the same IP subnet otherwise you need a router.

IPv4 doesn't allow two hosts in two different IP subnets to talk to each other directly.

To be noted that IPv6 allows this.

About vlan bridging each vlan needs to have at least one L2 port in STP forwarding state.

Hope to help


rakesh.hegde Sun, 05/31/2009 - 12:20

Hi Rupesh,

Fallback bridging bridges traffic that the switch can not route. For example, you can bridge IPV6 on a 3550 since it can not route IPV6.



Giuseppe Larosa Mon, 06/01/2009 - 02:10

Hello Rakesh,

other platforms like C6500 can perform vlan bridging for ipv4 by adding

bridge-group 1 bridge ip

C3550 and probably other C3x50 behave like you have described

Hope to help


rakesh.hegde Mon, 06/01/2009 - 13:11

Hi Giuseppe ,

You are right. 6500 behaves more like a router when it comes to bridging. Unlike Fallback bridging, we need to enable IRB to get it working. The command bridge-group <> bridge ip is enabled by default.



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