Route Reflectors—for Added Hierarchy

To use route reflection in an AS, you designate one or more routers as a route reflector—typically, one per point of presence (POP). Route reflectors have the special BGP ability to readvertise routes learned from an internal peer to other internal peers. So rather than requiring all internal peers to be fully meshed with each other, route reflection requires only that the route reflector be fully meshed with all internal peers. The route reflector and all its internal peers form a cluster, as shown in Figure 53.

You must have an Advanced BGP Feature license installed on each Services Router that uses a route reflector. For license details, see the J-series Services Router Administration Guide.

Figure 53 shows router RR configured as the route reflector for cluster 127. The other routers are designated internal peers within the cluster. BGP routes are advertised to router RR by any of the internal peers. RR then readvertises those routes to all other peers within the cluster.

You can configure multiple clusters and link them by configuring a full mesh of route reflectors (see Figure 54).

Figure 54 shows route reflectors RR1, RR2, RR3, and RR4 as fully meshed internal peers. When a router advertises a route to reflector RR1, RR1 readvertises the route to the other route reflectors, which, in turn, readvertise the route to the remaining routers within the AS. Route reflection allows the route to be propagated throughout the AS without the scaling problems created by the full mesh requirement.

However, as clusters become large, a full mesh with a route reflector becomes difficult to scale, as does a full mesh between route reflectors. To help offset this problem, you can group clusters of routers together into clusters of clusters for hierarchical route reflection (see Figure 55).

Figure 55 shows RR2, RR3, and RR4 as the route reflectors for clusters 127, 19, and 45, respectively. Rather than fully mesh those route reflectors, the network administrator has configured them as part of another cluster (cluster 6) for which RR1 is the route reflector. When a router advertises a route to RR2, RR2 readvertises the route to all the routers within its own cluster, and then readvertises the route to RR1. RR1 readvertises the route to the routers in its cluster, and those routers propagate the route down through their clusters.