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Multihomed BGP seperate table announce to customers?

hi

Consider the topology attached. R1 is my router, and takes full anounces from R2 and R3. And R4 and R5 are my customers. What i will ask is can i distribute the full anounce that R1 learned from R2 to R4 and the full anounce learned from R3 to R5? Note that R2 and R3 have different paths. What i observe is BGP takes the best paths and only anounces the best path. When i look my bgp table by sh ip bgp i see there are multiple paths for every destination. But i can not seperate them and anounce to different customers. Are there any way to do this? I need to take full bgp table and anounce full bgp to customers. I can not anounce default route or specific selected routes, load share or backup. Neither is allowed. It can be done by two routers actually at AS700 but what i need to learn is that are there any ways to do this with single router.

Best Regards,

4 REPLIES
New Member

Re: Multihomed BGP seperate table announce to customers?

Hi,

I could not open your attachment, I think it has expired. However, it would be a violation of BGP Operation for a BGP speaker to advertise to neighbors any routes that it did not itself consider as best. Thats how BGP operates. If your BGP speaker has selected some of the routes as best and disregarded the updates from other sources, you still have a full routing table. The only way I can think of to do what you are trying to do is to make your BGP speaker consider all these updates from the different neighbors as equal so that they all get to be treated as best. To achieve this you have to check in your BGP table what attribute was used to descriminate one route from the other, then manipulate that attribute to equal the attributes of what BGP has considered as best. Then you would have to configure bgp maximum-paths to a value greater than the default of one so that all these " best " routes are installed in your Loc-RIB. Only then will BGP advertise all these to neighbors.

Herbert.

Cisco Employee

Re: Multihomed BGP seperate table announce to customers?

You could actually do this using two different VRFs. One for R2-R4 and another one for R3-R5.

The interface for R2 and R4 would be configured as part of VRF1 and would then share the same RIB. R3 and R5 could share VRF2.

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 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
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New Member

Re: Multihomed BGP seperate table announce to customers?

Hi

Thanks for your message. But can you give an example config or web link? As I understand i need to reconfigure customer router according to VRF which is hardly possible.

Regards.

Re: Multihomed BGP seperate table announce to customers?

Hello,

what Harold meant is to reconfigure only R1 to support VRF. Be aware, that this means more memory consumption and NO interconnection between R4 and R5.

Additionaly there will be no more entry in the global BGP table in R1. This seems somewhat problematic once R1 peers with other BGP speakers as well - especially with iBGP. So if you consider this option, be aware of the impacts.

Another option would be:

R2 and R4 in global BGP on R1

R3 and R5 in a separate VRF (isolated from R2 and R4) on R1

The cleanest solution from a BGP perspective:

connect R2 and R4 to R1

connect R3 and R5 to R6 (new/different router)

You can achieve your goals through utilizing weight in a matter, that R1 prefers R2 and R4 pathes and R6 prefers R3 and R5 pathes.

Hope this helps! Please rate all posts.

Regards, Martin

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