Juniper JUNOSE, Configuration Manual

Page: 184 / 738

Configuring Route Reflectors
Router reflection is an alternative to confederations as a strategy to reduce IBGP
meshing. BGP specifies that a BGP speaker cannot advertise routes to an IBGP
neighbor if the speaker learned the route from a different IBGP neighbor. A
route
reflector is a BGP speaker that advertises routes learned from each of its IBGP
neighbors to its other IBGP neighbors; routes are reflected among IBGP routers that
are not meshed. The route reflector’s neighbors are called
route reflector clients . The
clients are neighbors only to the route reflector, not to each other. Each route reflector
client depends on the route reflector to advertise its routes within the AS; each client
also depends on the route reflector to pass routes to the client.
A route reflector and its clients are collectively referred to as a cluster . Clients peer
only with a route reflector and do not peer outside their cluster. Route reflectors peer
with clients and other route reflectors within the cluster; outside the cluster they peer
with other reflectors and other routers that are neither clients nor reflectors. Route
reflectors and nonclient routers must be fully meshed.
Clients and nonclients have no knowledge of route reflection; they operate as standard
BGP peers and require no configuration. You simply configure the route reflectors.
Route reflectors advertise routes learned from:
■
A nonclient peer only to clients
■
A client peer to all nonclient peers and to all client peers except for the originator
of the route
■
An EBGP peer to all nonclient peers and all client peers
Figure 43 on page 149 illustrates a simple route reflection setup. Configured as a route
reflector, Router Harvard reflects routes among its clients within Cluster 23: Routers
Plymouth, Westford, and Acton. These route reflector clients see router Harvard and
each other simply as IBGP neighbors. Router Newport in AS 325 and router Mason
in AS 413 see router Harvard simply as an EBGP neighbor in AS 29.
148 ■
Managing a Large-Scale AS
JUNOSe 11.0.x BGP and MPLS Configuration Guide