Setup Guide

Route Reectors
Route reectors reorganize the iBGP core into a hierarchy and allow some route advertisement rules.
NOTE: Do not use route reectors (RRs) in the forwarding path. In iBGP, hierarchal RRs maintaining forwarding plane RRs could
create routing loops.
Route reection divides iBGP peers into two groups: client peers and nonclient peers. A route reector and its client peers form a route
reection cluster. Because BGP speakers announce only the best route for a given prex, route reector rules are applied after the router
makes its best path decision.
• If a route was received from a nonclient peer, reect the route to all client peers.
• If the route was received from a client peer, reect the route to all nonclient and all client peers.
To illustrate how these rules aect routing, refer to the following illustration and the following steps. Routers B, C, D, E, and G are members
of the same AS (AS100). These routers are also in the same Route Reection Cluster, where Router D is the Route Reector. Router E and
H are client peers of Router D; Routers B and C and nonclient peers of Router D.
Figure 25. BGP Router Rules
1 Router B receives an advertisement from Router A through eBGP. Because 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 nonclient peer.
4 Router D does reect 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.
Conguring BGP Route Reectors
BGP route reectors are intended for ASs with a large mesh; they reduce the amount of BGP control trac.
NOTE
: Dell EMC Networking recommends not using multipath and add path simultaneously in a route reector.
With route reection congured properly, IBGP routers are not fully meshed within a cluster but all receive routing information.
Congure clusters of routers where one router is a concentration router and the others are clients who receive their updates from the
concentration router.
To congure a route reector, use the following commands.
• Assign a cluster ID or an IP address to a router reector cluster.
CONFIG-ROUTER-BGP mode
Border Gateway Protocol (BGP)
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