When all of the links within the TransitNet backbone have been enabled for MPLS, the last step of the migration is to remove any unnecessary BGP sessions. With the introduction of new route reflectors to propagate routes between POPs, the core routers are no longer needed to perform the route reflection task. They also do not need to carry BGP routes because they will label-switch all traffic that is directed toward external destinations. This is also true of the border routers within each POP.
Figure 6-5 shows the necessary BGP sessions, with all unnecessary sessions removed.