BGP Route Reflector
To solve this problem, BGP introduced a route reflector (RR). Instead of having every router peer with every other router in an AS, each router peers only with the RR. Advertisements are sent to the route reflector, which are then "reflected" out to all other BGP speakers.
A route reflector will only reflect routes that are considered "best routes", and it is not allowed to change any reflected route attributes, including the next hop IP address.
An RR will use the Cluster ID to prevent loops within the topology.