Explanation/Reference:
Explanation:
Route Reflectors
iBGP requires that all routers be configured to establish a logical connection with all other iBGP routers.
The logical connection is a TCP link between all iBGP-speaking routers. The routers in each TCP link
become BGP peers. In large networks, the number of iBGPmeshed peers can become very large. Network
administrators can use route reflectors to reduce the number of required mesh links between iBGP peers.
Some routers are selected to become the route reflectors to serve several other routers that act as route-
reflector clients. Route reflectors allow a router to advertise or reflect routes to clients. The route reflector
and its clients form a cluster. All client routers in the cluster peer with the route reflectors within the cluster.
The route reflectors also peer with all other route reflectors in the internetwork. A cluster can have more
than one route reflector.
Confederations
Another method to reduce the iBGP mesh within an autonomous system is BGP confederations. With
confederations, the autonomous system is divided into smaller, sub autonomous systems, and the whole
group is assigned a confederation ID. The sub-ASNs or identifiers are not advertised to the Internet but are
contained within the iBGP networks. The routers within each private autonomous system are configured
with the full iBGP mesh. Each sub-autonomous system is configured with eBGP to communicate with other
sub-autonomous systems in the confederation. External autonomous systems see only the ASN of the
confederation, and this number is configured with the BGP confederation identifier.