background image
Route Reflectors
many circuits or connections you will need in a full-mesh network by using
the formula n(n-1)/2. This means that for 20 routers, there are 190 circuits
or connections between the routers. Let's look at Figure 9.1 to see a full-
mesh network.
F I G U R E 9 . 1
A small full-mesh network
In a normal network, split-horizon rules mean that if we have two routers,
one named RouterA and another named RouterB, when RouterA sends
RouterB an update, RouterB will never send that information back to
RouterA. BGP split-horizon rules mean that if an iBGP peer in AS 100 sends
an update to a peer in AS 200, it will never send another router in AS 200 the
same update. This is the reason for the full mesh in the internal network--
so that all the routers in the network can share information they have learned
with one another.
Having 190 connections or peers in a network can be a problem, how-
ever--not just the severe cost, but the overhead on the routers that are send-
ing updates to one another. You can configure one router as a concentration
router to handle all of the BGP updates. Making a router a route reflector
places the main concentration of your configuration on only one router and
eliminates the need for a full mesh.
The route reflector is allowed to propagate iBGP routes to other iBGP
peers. Route reflectors can be very beneficial when ISPs use a considerable
number of internal neighbor statements. The concentration router needs to
be the only router configured with neighbor statements and becomes the
Full mesh
Copyright ©2001 SYBEX , Inc., Alameda, CA