iBGP problem - how to pass eBGP route to other iBGP neighbor?

[Leo Liu]

Dear all,

I have 3 routers (RT01, RT02 and RT03) running iBGP (AS-1001) and Each router connects to a eBGP neighbor(RT-A, RT-B and RT-c). (topology is as attached PNG file)

Problem I encounter is:

RT01 can get routing information from RT02 itself and RT-B(AS-1003)

RT03 can get routing information from RT02 itself and RT-B(AS-1003)

RT02 can get all routing information from both RT03 including RT-C and RT01including RT-A

but

RT01 can not get routing information from RT03 including routing from RT-C(AS-1004)

RT03 can not get routing information from RT01 including routing from RT-A(AS-1002)

I think it is because RT02 does not advertise routing information which is learned from one neighbor to another iBGP neighbor. (i.e. RT02 does not pass routing learned from RT03/RT-C to RT01, and also does not pass routing learned from RT01/RT-A to RT03)

any advice how to resolve it will be appreciated. Thanks!

[cadet alain · Accepted solution]

Hi,

in your AS 1001, just do a full mesh of iBGP neighbours: r1-r2,r1-r3,r2-r3

Regards

Alain

Don't forget to rate helpful posts.

[Stefano Sasso · Accepted solution]

You have to use a iBGP full mesh, or configure R2 as route-reflector.

bests

stefano

[neil grant · Accepted solution]

stefano and alain are correct,

bgp rules state an ibgp neighbour will not advertise ibgp learned routes to another ibgp peer, (without the above suggestions or confenderations)

Regards Neil 

http://uk.linkedin.com/pub/neil-grant/20/5b0/267

[Rick Morris · Accepted solution]

There is not really much else to add to what has already been stated, but I did find a link that may help provide more details:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml

[Leo Liu]

Thanks all for prompt response and clear clarification.

Since RT01 locates in different site and is unable to do full mesh with other iBGP neighbors, I will study all the information you provided first and try to configure R2 as route-reflector as adviced.

Thanks!!