Interprovider VPN Example—MP-EBGP Between ISP Peer Routers

In this example, all routes learned from the CE routers are sent over both service provider networks as VPN-IPv4 routes. The routes are initially learned by the PE routers (Router B and Router E) from the CE routers (Router A and Router F) and are announced by the PE routers to the AS border routers (Router C and Router D). The AS border routers are then configured with an MP-EBGP session, enabling them to pass the VPN-IPv4 routes with each other. When an AS border router—Router C for example—learns VPN-IPv4 routes from an internal BGP (IBGP) PE, the following occurs:

1. Router C sets itself as the next hop for the route and creates a label for that route.
2. Router C advertises the VPN-IPv4 route to PE Router D in AS 10045.
3. Router D sets the next hop to itself, creates another label, and then forwards the label and the route to its IBGP PE router (Router E).

This example has scaling limitations because of restrictions on the number of labels each PE router needs to allocate at the AS border.

Figure 51 illustrates the network topology used in this VPN example.

Figure 51: Network Topology of Interprovider VPN Example

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