Cisco Systems 1400 series, 1600R manual Sham-Link Example, Vpnv4 all tag begin

OSPF Sham-Link Support for MPLS VPN

Feature Overview

The following example shows the forwarding that occurs between sites from the standpoint of how PE-1 views the 10.3.1.7/32 prefix, the loopback1 interface of the Winchester CE router in Figure 4.

PE-1#show ip bgp vpnv4 all 10.3.1.7

BGP routing table entry for 100:251:10.3.1.7/32, version 124 Paths: (1 available, best #1)

Local

10.3.1.2 (metric 30) from 10.3.1.2 (10.3.1.2)

Origin incomplete, metric 11, localpref 100, valid, internal, best

Extended Community: RT:1:793 OSPF DOMAIN ID:0.0.0.100 OSPF RT:1:2:0 OSPF 2

PE-1# show ip route vrf ospf 10.3.1.7 Routing entry for 10.3.1.7/32

Known via "ospf 100", distance 110, metric 13, type intra area Redistributing via bgp 215

Last update from 10.3.1.2 00:12:59 ago Routing Descriptor Blocks:

10.3.1.2 (Default-IP-Routing-Table), from 10.3.1.7, 00:12:59 ago

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 reason the OSPF route is not redistributed to BGP on the PE is because the other end of the sham-link already redistributed the route to BGP and there is no need for duplication. The OSPF sham-link is used only to influence intra-area path selection. When sending traffic to a particular destination, the PE router uses the MP-BGP forwarding information.

Cisco IOS Release 12.2(8)T

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