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New Member

IBGP Design

I'm looking for some input on ibgp design. We have three c7500s routing ibgp - we'll call them routers A, B, and C. Router A is a route reflector; and routers B and C are reflector-clients. Each of these routers have EBGP connections to peering partners.

Now, I have a fourth router, a c7200, we'll call it router F, that will have an EBGP connection to another peering partner. We want to set up IBGP with router F and A, B, and C. But there are two hops between router F and the three other routers.

Our topology looks something like this:

F

|

|

E

|

|

D

|

|

C (client)

/

/

A (reflector)

\

\

B (client)

We intend to follow the physcial paths with our IBGP sessions. But do we have to run IBGP on router E and D as well?

3 REPLIES
New Member

Re: IBGP Design

You may not need to run BGP on all of the routers. As long as you have not disable synchronization then you should be all set, I would just add Router F as a reflector client to A (note, you will need and IGP or static routes running on all 5 routers)

If you have disabled synchronization, as most people do without even thinking about it, then yes you will need to run iBGP on all 5 routers in a full mesh, or route-reflector, topology.

I hope this helps.

Cisco Employee

Re: IBGP Design

You are assuming that they redistribute BGP routes in the IGP, which is not the case in most designs.

If they don't redistribute BGP routes in the IGP, then they'd probably be better off running BGP on D and E as well.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
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México
Gold

Re: IBGP Design

Yes, you will need to run iBGP on all of these routers. The best thing would be to make them all reflector clients of the reflector you are already planning on using, I would think.

Otherwise, when F forwards a packet to E, how will E know where to forward it? You can't use a default route, since the default can't work in both directions. You'll need the BGP routing table to correctly route each destination.

:-)

Russ.W

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