BGP Route reflector and load balancing

[mautez_mah]

hi Team 
I have some questions about BGP if you please :
1- if we have in our environment BGP domain one cluster for two RR, and as we know RR once receive a packet will generate two attributes to prevent loop ( originator and cluster list ) so now what is the difference between both of them ( if we are in the same domain ) and there is only one cluster,
2- what is the difference between ( max-path, multiple iBGP sessions on the RR. and add-path) 
3- is there any article explain the problem we may face using RR or confederations we can understand these technical deeper 

[MHM Cisco World]

http://thebest.network-solution.net/2015/09/bgp-route-reflector-rr.html

[Giuseppe Larosa]

Hello @mautez_mah  ,

when you use two RR servers serving the same set of clients you have two design choices:

1) use the same cluster-id on both

2) use a different cluster-id on the two RRS

The second choice will generate more reflected advertisements as the two RRS will see each other as not being in the same "cluster".

However, this second choice allows to cover some fault cases that choice 1) is not able to cover: if there are two clients X and Y with X having lost the iBGP session with RRS2 and Y having lost the iBGP session with RRS1 the exchange of routes between X and Y still happens going via the two RRS because of the different cluster-id.

About your other questions:

Both RRS will choice the same best path so each client will select as best path the one coming from the device with lowest BGP RID.

Hope to help

Giuseppe

[mautez_mah]

@Giuseppe Larosa  many thanks 
just can u explain more plz "Both RRS will choose the same best path so each client will select as the best path the one coming from the device with the lowest BGP RID. I know each client will install the best route from RR , 

[Giuseppe Larosa · Accepted solution]

Hello @mautez_mah ,

I was referring to the case where the route reflector client reiceves the best path via two different RRS, in this case the route propagated by the RRS with the lowest BGP RID is preferred and selected as best

And even if it is not reported  in the best path BGP selection in Cisco documents the Cluster List attribute is used to select the best path.

Hope to help

Giuseppe