eBGP connections don't use the same rules as ibgp. When using ibgp, the ibgp neighbor cannot advertise an ibgp learned route to another ibgp neighbor. This is why it requires a full mesh or route reflectors in order to workaround those rules. Your diagram, however, is an ibgp neighbor advertising to another ibgp neighbor, which then CAN advertise to an ebgp neighbor. You can avoid this if you want by setting the community local-as or no-export, or configuring an outbound route-map on R5 that matches the route and denies it from being advertised to your ebgp peer.
As John already explained this is normal behaviour and you'll have to filter this route on R5 if you don't want it to go to R2( using a route-map or a prefix-list or distribute-list outbound) or you can use community(setting it to local AS or no-export) when advertsing it to R5 with the network command using a route-map and sending the community to R5.
it means eBGP doesn't care, it'll take any route from anyone unless we specifically configured to ignore routes.. Thats why i am seeing routes in R2 which is advertised in R12 iBGP. please let me know if my understanding is correct.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...