Thursday, August 18, 2011

Configuring BGP - Route Reflectors

To route reflect, or not to route reflect, that is the question. If a full iBGP mesh is required then consider Route Reflectors. If you had to iBGP full mesh 10 sites you would need 45 iBGP connections (10*(9)/2 or n * (n-1)/2 where n is the # of sites) = NIGHTMARE!!! In this blogtorial I will show you how to deploy a route reflector and drastically reduce the number of connections needed to achieve the same results as a full iBGP mesh design. 

Consider the simple topology and let's get started. 

Relevant configurations are posted below.
iBGP learned routes will not be advertised to other iBGP peers and therefore you would need an iBGP full mesh design. This article is a good read on why this is the case. iBGP full mesh design does not scale well which is where route reflectors come in. 

Let's get R2, R3, R4 interfaces and BGP configured. 

Now let's get the R1 (Route Reflector Configured) and see how the routes are advertised. 

Let's verify the routes on R1, R2, R3, and R4. Notice how all the routes are making it into all the routers. 

Now notice how they also show up as an iBGP learned route. 

As you can see route reflectors can avoid iBGP full mesh designs. With the route reflectors iBGP learned routes can be advertised to other iBGP peers. 

Do a 'clear ip bgp *' on all routers or a specific router if something does not function properly. 

Many more articles to come so stay tuned and "Join this site" on the right.

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