Cisco Systems 1400 series, 1600, 1600R manual 6

OSPF Sham-Link Support for MPLS VPN
Feature Overview
6
Cisco IOS Release 12.2(8)T
Figure 4 Sham-Link Example
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.
PE-1# show ip bgp vpnv4 all tag | begin 10.3.1.7
10.3.1.7/32 10.3.1.2 notag/38
PE-1# show tag-switching forwarding 10.3.1.2
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
31 42 10.3.1.2/32 0 PO3/0/0 point2point
MPLS VPN Backbone
Area 1
Winchester
10.3.1.7
Brighton
70393
PE-3
10.3.1.2
PE-2
10.3.1.5
PE-1
10.3.1.6
Sham-link
Sham-link
Area 1
Stockholm
10.3.1.3
Area 1 Vienna
10.3.1.15