164 | Border Gateway Protocolw w w . d e l l . c o m | s u p p o r t . d e l l . c o m Route ReflectorsRoute Reflectors reorganize the iBGP core into a hierarchy and allows some route advertisement rules.Route reflection divides iBGP peers into two groups: client peers and nonclient peers. A route reflector andits client peers form a route reflection cluster. Since BGP speakers announce only the best route for a givenprefix, route reflector rules are applied after the router makes its best path decision.• If a route was received from a nonclient peer, reflect the route to all client peers.• If the route was received from a client peer, reflect the route to all nonclient and all client peers.To illustrate how these rules affect routing, see Figure 8-3 and the following steps. Routers B, C, D, E, andG are members of the same AS - AS100. These routers are also in the same Route Reflection Cluster,where Router D is the Route Reflector. Router E and H are client peers of Router D; Routers B and C andnonclient peers of Router D.Figure 8-3. Route Reflection Example1. Router B receives an advertisement from Router A through eBGP. Since the route is learned througheBGP, Router B advertises it to all its iBGP peers: Routers C and D.2. Router C receives the advertisement but does not advertise it to any peer because its only other peer isRouter D, an iBGP peer, and Router D has already learned it through iBGP from Router B.3. Router D does not advertise the route to Router C because Router C is a nonclient peer and the routeadvertisement came from Router B who is also a non-client peer.4. Router D does reflect the advertisement to Routers E and G because they are client peers of Router D.5. Routers E and G then advertise this iBGP learned route to their eBGP peers Routers F and H.Note: Route Reflectors (RRs) should not be used in the forwarding path. In iBGP, hierarchal RRsmaintaining forwarding plane RRs could create routing loops.Router A Router BRouter CRouter DRouter ERouter GRouter FRouter H{eBGP Route{eBGP Route{eBGP RouteRoute Reflector Route Reflector Client PeersiBGP RouteiBGP RoutesiBGP Routes
