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BVI 12 years 3 months ago #17976

  • Pforty
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Can someone explain how IRB works with the BVI on a cisco layer 3 switch?

Would IRB be a better solution than interVlan routing for connecting Vlans that are local to the layer 3 switch ?

Re: BVI 12 years 3 months ago #17980

  • Dove
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Hi, am not familier with this topic. Its new to me but when I try to read about this I found the below details. Hope it will helps u.


[b]Integrated Routing and Bridging[/b]
Your network might require you to bridge local traffic within several segments while having hosts on the bridged segments reach the hosts or routers on routed networks. For example, if you are migrating bridged topologies into routed topologies, you might want to start by connecting some of the bridged segments to the routed networks.

Using the integrated routing and bridging (IRB) feature, you can route a given protocol between routed interfaces and bridge groups within a single Catalyst 4840G SLB switch. Specifically, local or unroutable traffic is bridged among the bridged interfaces in the same bridge group, while routable traffic is routed to other routed interfaces or bridge groups.

Because bridging is in Layer 2 and routing is in Layer 3, they have different protocol configurations. With IP, for example, bridge group interfaces belong to the same network and have a collective IP network address. In contrast, each routed interface represents a distinct network and has its own IP network address. Integrated routing and bridging uses Bridge-Group Virtual Interface (BVI) to enable these interfaces to exchange packets for a given protocol.

A BVI is a virtual interface within the campus Catalyst 4840G SLB switch that acts like a normal routed interface. A BVI does not support bridging, but actually represents the corresponding bridge group to routed interfaces within the switch. The interface number is the link between the BVI and the bridge group.

Layer 3 switching software supports the routing of IP between routed interfaces and bridged interfaces in the same router, in both fast-switching and process-switching paths.



Re: BVI 12 years 3 months ago #18011

No wonder people don't understand with an explaination like that. what a load of nonsense.

No disrespect Dove, nice of you to try to help.

Re: BVI 12 years 3 months ago #18024

  • jwj
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Ok, let's try and not start a flame war here...

On to the question, Inter-VLAN routing will give you the best performance on a layer 3 switch. It's specifically what they are made for.

Now, onto Integrated Routing and Bridging (IRB). Basically what this does, is allows you to group layer 2 segments into "bridge groups" that are routed by the BVI interface. You can have multiple bridge groups, and mutiple BVI's, but they all correlate to each other. Ex. bridge group 1 uses BVI1, bridge group 2 use BVI2, etc. Other than that what Dove posted has good information on IRB. One final note, I personally have only seen/used IRB on DSL routers or other WAN connected routers. I guess you could do it on a switch, but inter-vlan routing is so much more simpler and elegant, IMO.

Re: BVI 12 years 3 months ago #18033

  • Pforty
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Thank JWJ,
Sorry about the additional postings, needed answers by examples.

Re: BVI 12 years 3 months ago #18049

Yeah, im sorry if I was a bit negative there.

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