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BGP session between RRs


I have a question. I have MPLS VPNs created via two route-reflectors. Initally a have BGP sessions only between PEs and RRs. Everything is ok. But do I need BGP session between RRs?

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BGP session between RRs

From your description I have the understanding that you have 2 routers running BGP to 2 PE routers. It is not clear whether the routers running BGP have RR clients configured. Perhaps a better understanding of your topology would allow us to give you better answers. But in general if you have 2 routers running BGP to PE routers then you should have BGP sessions between these two routers.



BGP session between RRs

Ok))) I have many many PEs. And two RRs. Each PE has BGP session with both RRs. Extensions for VPNv4 are turned on. My question is do I need BGP session between RRs for some reason? This session may be needed I think since there is special attribute called Cluster-id so we need this session for some situations but I cant understand when and why? Am I clear now?

BGP session between RRs

From a Design Prespective, it can add another layer of redundancy!  It can also be used to send EBGP updates if you have an EBGP neighbors connected to one of the RRs.

however, it all depends on your current design, but in general, a BGP Session between RRs in the Same Cluster wont impact your design.

In other words, Clients can peer with 2 or more route reflectors in the Same Cluster where the RRs in this same cluster also have an IBGP Session between them.

However, clients dual homed to RRs in different Clusters,ie: connected to 2 RRs in different clusters, the RRs in this case  should not have an IBGP Session between them.

Remember, RRs will reject update that contains the same Cluster id as the first factor, and as last resort reject BGP update that contains the same originator id.



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