MPLS-Enabled Applications: Emerging Developments and New Technologies

8.4. ROUTE REFLECTORS AND VPNs

Let us now turn to the last remaining component of the VPN solution: route reflectors. The functional requirements and the tradeoffs regarding the use of route reflectors (RRs) are different in a VPN scenario than in a pure IP (Internet routing) scenario. In both cases the RR provides the following benefits from the configuration management point of view:

• Reduction in the number of BGP peerings. A BGP speaker (e.g. a PE) only needs to peer with the RR rather than with all other BGP speakers. Thus, each speaker maintains a constant number of peerings, regardless of the number of BGP speakers in the network.

• Ease of configuration. Adding a new BGP speaker only requires setting up a BGP session to the RR, rather than multiple sessions from and to the new speaker.

The differences in the RR use in plain IP service provider networks and VPN networks stem from differences in the routing information carried and how it is advertised, in particular:

1. The routes carried by the PE routers.

2. The number of paths to a particular destination.

In a pure IP scenario, the routing information carried in BGP is the full Internet routing table. Traffic is forwarded as IP and therefore:

1. All routers need to have information for all the destinations.

2. Multiple paths exist for the same destination, because providers typically have several external peerings over which they learn Internet routes.

In this setup, the RR is often used to perform path selection, with the following consequences: ...