The route reflector and its clients form a cluster, using the unique Cluster ID in the AS as an identifier. When a route is reflected by the RR for the first time, if there is no Cluster_List…

The route reflector and its clients form a cluster, using the unique Cluster ID in the AS as an identifier. When a route is reflected by the RR for the first time, if there is no Cluster_List attribute, the RR will add the local Cluster ID to the front of the Cluster_List. If a route already has the Cluster_List attribute, the RR will no longer modify the Cluster_List attribute.