MPLS-Enabled Applications: Emerging Developments and New Technologies

7.4. THE PEER VPN MODEL

The problems of the overlay model stem from the fact that customer routers peer directly with each other. The peer model attempts to overcome the drawbacks of the overlay model by lifting the requirement for direct routing exchanges between the customer routers. Instead of peering with each other and forming an overlay on top of the service provider's network, CE routers now peer only with directly attached PE routers. As a result, the large mesh of routing peerings between CE routers disappears. From the customer's point of view, routing becomes very easy. The burden of managing the route distribution between the customer sites is now passed on to the provider and the intelligence moves out of the CE routers into the PE routers.

Moving from a CE-based solution to a PE-based one has other benefits as well:

• Adding a new customer site to a VPN requires configuration of the CE and PE for the new site only, rather than configuration of all the customer's CEs.

• The number of points of control in the network (i.e. the number of intelligent devices that make meaningful routing decisions) does not necessarily increase for each new customer site added (assuming that more than one CE can attach to the same PE and that the CE can simply run static routing).

• A single infrastructure is used to service all VPN customers.

• The exact traffic matrix between customer sites is not required in order to provision bandwidth between customer sites. Instead, it is enough to know the ...