Interface I never used

[mrashby]

All,

I was working with one of my colleagues to set up a configuration between two routers. After it was all done I noticed he used a BVI inverface, what is an BVI interface and why do you have to run the bridge irb command before you can activate it. Thanks.

[Josef Oduwo]

A BVI interface is a virtual interface within the campus switch router that acts like a normal routed interface. A BVI does not support bridging, but it actually represents the corresponding bridge group to routed interfaces within the switch router.

Using the integrated routing and bridging (IRB) feature, you can route a given protocol between routed interfaces and bridge groups within a single switch router. Specifically, local or unroutable traffic will be bridged among the bridged interfaces in the same bridge group, while routable traffic will be routed to other routed interfaces or bridge groups.

There are two major steps to configuring IRB:

1. Configure bridge groups and routed interfaces (including enabling and configuring bridging and routing):

Router(config)#bridge bridge-group protocol {ieee | dec} etc

2. Then configure IRB and the BVI (which covers enableing IRB followed by configuring BVI).

The bridge irb commands falls is this section. It enables IRB, allowing routing of traffic from the bridged interfaces:

Router(config)#bridge irb

So to answer your question, the bridge irb command doesn't come before "activate" BVI, it is the actual activation command...

I hope this helps,

Josef.

[amit-singh]

Hi,

BVI is the bridge virtual interface and we define it for integrated routing and briding. Irb stands for intergrated routing and briding. If you have same vlan across a router interface then you can enable IRB to bridge both the vlans and to be used as a single Vlan and bridge your local traffic over the routed network.

http://www.cisco.com/univercd/cc/td/doc/product/ong/15400/r40docs/454ios40/irb.htm

HTH,

-amit singh

[Richard Burts]

To understand the BVI I think a little history is helpful. In the older versions of IOS the decision of whether a protocol was routed or bridged was a global decision. You could route IPX or you could bridge it. But it had to be treated the same on all interfaces. You could route IP or you could bridge IP but it had to be the same on all interfaces.

Integrated Routing and Bridging (IRB) was an enhancement to IOS which allows the decision of whether to route or to bridge to be made at the interface rather than made globally. This means that the protocol (IPX or IP or whatever) can be routed on some interfaces and bridged on other interfaces. Part of what makes this work is the BVI. The BVI is a virtual interface which provides the linkage between the routed environment and the bridged environment. (It is how data from bridged intefaces gets to the routed ones, and how data from routed interfaces gets to the bridged ones.)

HTH

Rick

[mrashby]

Okay now I see but to bring it all home when you say bridged traffic I take it you are talking about layer 2 traffic and routed traffic is layer 3 traffic.

[Josef Oduwo]

Yes, bridged traffic is always at Layer 2 and routed traffic is at Layer 3...

Josef.