Administrator Guide

Route Reflectors
Route reflectors reorganize the iBGP core into a hierarchy and allow some route advertisement rules.
NOTE: Do not use route reflectors (RRs) 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. Because 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, 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 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 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 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.
Configuring BGP Route Reflectors
BGP route reflectors are intended for ASs with a large mesh; they reduce the amount of BGP control traffic.
NOTE: Dell EMC Networking recommends
not using multipath and add path simultaneously in a route reflector.
With route reflection configured properly, IBGP routers are not fully meshed within a cluster but all receive routing information.
Configure clusters of routers where one router is a concentration router and the others are clients who receive their updates from the
concentration router.
To configure a route reflector, use the following commands.
• Assign a cluster ID or an IP address to a router reflector cluster.
CONFIG-ROUTER-BGP mode
bgp cluster-id ip-address | number
• ip-address: IP address as the route reflector cluster ID.
• number: A route reflector cluster ID as a number from 1 to 4294967295.
You can have multiple clusters in an AS. When a BGP cluster contains only one route reflector, the cluster ID is the route reflector’s
router ID. For redundancy, a BGP cluster may contain two or more route reflectors. Without a cluster ID, the route reflector cannot
recognize route updates from the other routes reflector within the cluster.
• Configure the local router as a route reflector and the specified neighbors or peer group as members of the cluster.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-address | peer-group-name} route-reflector-client
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Border Gateway Protocol (BGP)