Handling Customer Routes
MPLS PE routers use a separate virtual routing instance for each customer,
called a Virtual Routing and Forwarding (VRF) table. Each customer router
advertises its routes to its PE router. C routers can use a standard routing
protocol to advertise their routes. The PE router looks like any other neighbor
to the C router. Because VRFs must be configured on the PE router, the
routing protocol needs to support them. EIGRP, OSPF, RIPv2, BGP, and
static routing support VRFs.
C routes are then advertised via Multiprotocol BGP (MP-BGP) to other PE
routers participating in that VRF. BGP runs only between the edge routers;
internal P routers use an Interior Gateway Protocol (IGP) such as OSPF or
EIGRP to tell them how to reach the PE routers. P routers have no knowledge
of customer routes. Thus, PE routers do the following types of routing:
■ IGP, BGP, or static routing with its customer routers to exchange IPv4
routes
■ MP-BGP with its peer PE routers to exchange VPNv4 routes
■ IGP with its neighboring P routers to exchange core network routes