IBGP session between RR in the same cluster

[CARLO CIANFARANI]

Hi,

I was thinking about the reason (if exist !) behind the IBGP session between RRs when configured in the same cluster-id.

Basically consider a cluster made of 2 RRs and RRCs each having sessions with the two RRs. RRs are configured in the same bgp cluster (for instance bgp cluster-id 1) . In this this scenario I've seen many times an IBGP session configured between two RRs.

Now, AFAIK, when RR advertise a RRC received NLRI it add the cluster-id value configured. So, excluding NLRI local originated or EBGP learned, the other RR will drop the update advertised on this IBGP session

Does it make sense ?

Thanks

[CARLO CIANFARANI]

Any answer in appreciated.

Thanks

[Peter Paluch · Accepted solution]

Hi Carlo,

If I understand you correctly then you are asking why should multiple RRs in a single cluster be peered in BGP. The basic reason is the same as with any iBGP peering - if one of the RRs learns about a new network via eBGP or via local injection, it needs to tell it to the other RR directly, as no RR client would do that.

Please feel welcome to ask further!

Best regards,

Peter

[CARLO CIANFARANI]

Great ! As you said and I supposed eBGP or locally injected networks are the only reasons for that iBGP session

Thanks a lot

[Peter Paluch]

Hi Carlo,

As you said and I supposed eBGP or locally injected networks are the only reasons for that iBGP session

Yes, but surely, that's reason enough!

Best regards,

Peter