CLUSTER_LIST prevents loops between multiple RR clusters. It should be obvious to you that this is the same loop prevention function that AS_PATH performs. If it sees its own cluster ID in the list, it knows that a routing loop has occurred and ignores the update.

When an RR receives an update, it checks the CLUSTER_LIST. If the CLUSTER_LIST is empty, the RR creates one. When a RR reflects a route from a client to a nonclient, it appends its cluster ID to the CLUSTER_LIST. As a result, ORIGINATOR_ID prevents loops within a single RR cluster.ĬLUSTER_LIST is an optional, nontransitive attribute (Type code 10) that tracks cluster IDs the same way that the AS_PATH attribute tracks AS numbers. A route reflector does not advertise a route back to the originator of the route nonetheless, if the originator receives an update with its own RID, the update is ignored.

The ORIGINATOR_ID is the router ID of the originator of a route within the local autonomous system. ORIGINATOR_ID is an optional, nontransitive attribute (Type code 9) that is created by the route reflector. In addition, to prevent routing loops, route reflectors use two BGP path attributes: ORIGINATOR_ID and CLUSTER_LIST. To avoid routing loops the route reflector cannot change the attributes of the routes it receives from its clients. The route reflector is indeed allowed to advertise routes it learns from one client to its other clients. Route reflectors work by relaxing the rule that iBGP peers cannot advertise routes learned from other iBGP peers. However, you can use both within the same AS if needed.

Route reflection is simpler to implement, both for the configuration statements needed and for topology issues.Ĭonfederations, as we will see later, add additional controls within the AS to manage it in more of an eBGP fashion, but at the cost of complexity.But only the route reflectors must understand route reflection the client routers see their connection to the RR as just another IBGP connection. All routers in a confederation must understand and support confederations.Route reflectors have two advantages over confederations: Route Reflectors are a way to reduce the number of iBGP peer connections in a large AS. BGP Prefix Independent Convergence (PIC).

Route reflector client