RR is configured as a route reflector redistributing routes among the connected internal peers. However, this requirement does not scale well when there are many iBGP speakers. You simply establish a BGP session from the route reflector to each internal peer and the iBGP full-mesh requirement is met.įigure 1 shows the configuration of a single cluster with one route reflector. BGP Route Reflector BGP requires that all iBGP speakers be fully meshed. A route reflector is not limited by the re-advertising restriction anymore, allowing it to share routes with other iBGP speakers. Using the route reflection principle you can designate one or several of your routers as route reflectors. iBGP neither has any loop prevention mechanism, and this is why you require route reflectors to be setup for large networks. Because of that, the routers should be fully interconnected, hence the full mesh requirement. BGP route reflection eliminates the need for a full IBGP mesh by allowing routers configured as route reflectors to re-advertise routes from one IBGP peer. The route reflector does not participate in autodiscovery that is, no pseudowires are set up between the route reflector and the provider edge (PE) devices. IBGP has the restriction of not allowing to redistribute the learned routes to other internal peers. A BGP route reflector can be used to reflect BGP EVPN prefixes without EVPN being explicitly configured on the route reflector. Route reflection enables sharing of routing information among multiple routers without having to send the exact same information to each of them individually. Route reflection comes to solve the complexity of multiple peering configuration. Therefore, in a large network, the full-mesh requirement for iBGP can be a big challenge. The formula to compute the number of sessions required for a full mesh is v (v - 1)/2, where v is the number of BGP-enabled devices. Because of the increasing numbers of iBGP sessions the possibilities of scaling are limited. Because of the internal BGP (IBGP) full-mesh requirement, most networks use route reflectors to simplify configuration. The typical fully-meshed iBGP configuration of routers can become very difficult to manage in large networks.
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