IRB

Answered Question
Feb 12th, 2007

Hello,

Is it possible to handle more VLANs with IRB. Because as I have seen BVI interface doesn't support subinterfaces, and VLAN tagging. I would like to have on fast ethernet 3 VLAN-s and ip address coresponding to those VLANa. Is it possible with IRB?

Thanks in advance

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Correct Answer by Richard Burts about 9 years 7 months ago

antonio

If I understand correctly what you need I would think that the solution would be to create 3 bridge groups and 3 BVI interfaces. Bridge-group 1 and interface BVI 1 for VLAN 1, Bridge-group 4 and interface BVI 4 for VLAN 4, and bridge-group 10 and interface BVI 10 for VLAN 10 (adjust for whatever your VLAN numbers are).

HTH

Rick

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glen.grant Mon, 02/12/2007 - 06:13

Do you need to bridge is the question. If not all you need to do is put the subinterfaces on the fastethernet interface and put the addresses on the subinterface and this will allow you to trunk down to switches with the appropriate trunking statements on the subinterfaces . . A little more info on what you are trying to do would help us help you .

Antonio_1_2 Mon, 02/12/2007 - 06:46

Yes I need bridging, because I need to connect router with two interfaces for redundancy, and spanning tree will keep one of interfaces in blocking state. Problem is that I have 3 VLANs.

Correct Answer
Richard Burts Mon, 02/12/2007 - 11:26

antonio

If I understand correctly what you need I would think that the solution would be to create 3 bridge groups and 3 BVI interfaces. Bridge-group 1 and interface BVI 1 for VLAN 1, Bridge-group 4 and interface BVI 4 for VLAN 4, and bridge-group 10 and interface BVI 10 for VLAN 10 (adjust for whatever your VLAN numbers are).

HTH

Rick

glen.grant Wed, 02/14/2007 - 06:35

Rick just a question for my knowledge , would he need multiple BVI's or just one BVI and put the same bridge group on all interfaces ?

Richard Burts Wed, 02/14/2007 - 13:56

Glen

If he defines a single BVI and a single bridge group and assigns the same bridge group on all interfaces then he bridges all the VLANs together and he really has a single VLAN and not 3 VLANs. A VLAN is a broadcast domain. When you bridge different interfaces together you are putting them into the same broadcast domain. If he wants to maintain 3 VLANs then he neds 3 BVIs.

HTH

Rick

glen.grant Wed, 02/14/2007 - 14:59

Guess i am a little confused as to what he wants, if he wants additional vlans why doesn't he just use additional subinterfaces on the fast ether . Bridging is normally used for unroutable protocols like LAT so he would not reallly have 1 vlan , he would still 3 vlans but with one bridge group for unroutable protocols with its own spanning tree .

Richard Burts Wed, 02/14/2007 - 17:11

Glen

I agree that there may be some confusion about what he is trying to do and it may be that my understanding is flawed. I believe that the key is in one of the follow up messages in which he says that he needs to bridge because he wants two interfaces on the router to be active in the same subnet (same VLAN) to provide redundancy. To get two interfaces in the same subnet/VLAN he needs to bridge and to bridge the interfaces and to route IP he needs IRB with BVI. And if he has 3 VLANs and wants to keep the 3 VLANs separate then he needs 3 BVIs (and 3 bridge groups).

HTH

Rick

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