The idea is to receive more than one path – i.e the best path calculate by the RR)
All routers are connected to the RR.
Extract of the configuration on the RR
router bgp 65000 bgp router-id 10.1.1.1 bgp log-neighbor-changes bgp additional-paths select best 2 bgp additional-paths send neighbor IBGP peer-group neighbor IBGP remote-as 65000 neighbor IBGP update-source Loopback0 neighbor IBGP route-reflector-client neighbor IBGP advertise additional-paths best 2 maximum-paths ibgp 2
The RR accepts two paths, and advertise additional paths on the same session.
Extract on one bgp client
router bgp 65000 bgp router-id 10.1.1.2 bgp log-neighbor-changes neighbor 10.1.1.1 remote-as 65000 neighbor 10.1.1.1 update-source Loopback0 neighbor 10.1.1.1 next-hop-self neighbor 10.1.1.1 additional-paths receive maximum-paths ibgp 2
The client supports two paths and could receive more than one path from the same neighbor.