Route Reflectors - Dell Force10 S4810P Configuration Manual

Route Reflectors

Route Reflectors reorganize the iBGP core into a hierarchy and allows some route advertisement rules.
Note: Route Reflectors (RRs) should not be used in the forwarding path. In iBGP, hierarchal RRs
maintaining forwarding plane RRs could create routing loops.
Route reflection divides iBGP peers into two groups: client peers and nonclient peers. A route reflector and
its client peers form a route reflection cluster . Since BGP speakers announce only the best route for a given
prefix, 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
G 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 and
nonclient peers of Router D.
Figure 9-3. Route Reflection Example
Router A
iBGP Route
1. Router B receives an advertisement from Router A through eBGP. Since the route is learned through
eBGP, 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 is
Router 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 route
advertisement 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.
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| Border Gateway Protocol
eBGP Route
Router B
Route Reflector
Router D
Router C
Figure 9-3 and the following steps. Routers B, C, D, E, and
Router E
iBGP Routes
Route Reflector Client Peers
Router G
iBGP Routes
eBGP Route
Router F
Router H
eBGP Route