BGP Route Reflector

[lagapidis (Lazarus Agapidis)]

Hello Unni

This topology shows an MPLS network where two of the P routers found within the core MPLS network function as route reflectors. This is done for BGP scalability within the MPLS network.

RRs either in a conventional or an MPLS network, are there to allow BGP to be scalable within a large network. It reduces the number of peerings necessary within the network. More on this can be found at the following post:

MPLS Labels and Devices

Hello Tanmoy The Route Reflector (RR) used in MP-BGP within an ISP’s MPLS network is used in a similar way to it’s purpose within a regular BGP AS. Within an AS, iBGP requires that all iBGP routers have full mesh neighbor adjacencies. This means that in an AS with, say, 10 iBGP speakers, we’ll need N(N-1)/2 or 10*(10-1)/2 = 45 adjacencies. As AS networks increase, these adjacencies increase in number almost exponentially, which is a problem for scalability. The solution for this is an RR. …

Now there are various ways that you can implement RRs within the MPLS network and these depend upon various factors. In this topology, it looks like the RRs are actually P routers that act both as RRs and as routers forwarding traffic as well. It is possible to have dedicated RRs that only function as RRs and don’t actually forward traffic. Other options include using the RRs for both IPv4 and VPNv4, or using them only for VPNv4 traffic.

A very comprehensive explanation of these concepts and the options available can be found at this link.

I hope this has been helpful!

Laz