Rt updating bgp 0 0 0 00
A sham-link ensures that OSPF client sites that share a backdoor link can communicate over the MPLS VPN backbone and participate in VPN services.
Flexible Routing in an MPLS VPN Configuration In an MPLS VPN configuration, the OSPF cost configured with a sham-link allows you to decide if OSPF client site traffic will be routed over a backdoor link or through the VPN backbone.
The PE router uses the information received from MP-BGP to set the ongoing label stack of incoming packets, and to decide to which egress PE router to label switch the packets.
Client Site Connection Across the MPLS VPN Backbone A sham-link overcomes the OSPF default behavior for selecting an intra-area backdoor route between VPN sites instead of an interarea (PE-to-PE) route.
Figure 4 Sham-Link Example The next example shows forwarding information in which the next hop for the route, 10.3.1.2, is the PE-3 router rather than the PE-2 router (which is the best path according to OSPF).
The following example shows BGP routing table entries for the prefix 10.3.1.7/32 in the PE-1 router in .
This prefix is the loopback interface of the Winchester CE router.
It is not possible to route traffic from one sham-link over another sham-link.
In the following example, PE-2 shows how an MP-BGP update for the prefix is not generated.