If a BGP router does not advertise the routes learned from one iBGP neighbor to another router

If Border Gateway Protocol (BGP) is not propagating any internal BGP (iBGP) learned routes to another iBGP peer because it requires a full iBGP mesh within the Autonomous System (AS). To overcome this issue you can configure BGP router as a route reflector

By configuring a BGP router to be a route reflector, a full mesh is no longer required. To configure a BGP router to be a route reflector, you can use the command ‘neighbor route-reflector-client’ command.

#neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client

ip-address-IP address of the BGP neighbor being added as a route reflector client
ipv6-address-IPV6 address of the BGP neighbor being added as a route reflector client
peer-group-name-Name of a BGP peer group name