Cisco Systems 1400 series, 1600R manual PE-1#show ip bgp vpnv4 all, From 0.0.0.0

OSPF Sham-Link Support for MPLS VPN

Feature Overview

Figure 2 Backdoor Paths Between OSPF Client Sites

MPLS VPN Backbone

PE-3

10.3.1.2

PE-1

10.3.1.6PE-2 10.3.1.5

Winchester

10.3.1.7Area 1

Brighton

70391

Area 1	Vienna	Stockholm	Area 1
	10.3.1.15	10.3.1.3

For example, Figure 2 shows three client sites, each with backdoor links. Because each site runs OSPF within the same Area 1 configuration, all routing between the three sites follows the intraarea path across the backdoor links, rather than over the MPLS VPN backbone.

The following example shows BGP routing table entries for the prefix 10.3.1.7/32 in the PE-1 router in Figure 2. This prefix is the loopback interface of the Winchester CE router. As shown in bold in this example, the loopback interface is learned via BGP from PE-2 and PE-3. It is also generated through redistribution into BGP on PE-1.

PE-1#show ip bgp vpnv4 all 10.3.1.7

BGP routing table entry for 100:251:10.3.1.7/32, version 58

Paths: (3 available, best #2)

Advertised to non peer-group peers:

10.3.1.210.3.1.5

Local

10.3.1.5(metric 30) from 10.3.1.5 (10.3.1.5)

Origin incomplete, metric 22, localpref 100, valid, internal

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

RT:1:2:0 OSPF 2

Local

10.2.1.38 from 0.0.0.0 (10.3.1.6)

Origin incomplete, metric 86, localpref 100, weight 32768, valid, sourced, best

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

Local

10.3.1.2 (metric 30) from 10.3.1.2 (10.3.1.2)

Origin incomplete, metric 11, localpref 100, valid, internal Extended Community: RT:1:793 OSPF DOMAIN ID:0.0.0.100 OSPF RT:1:2:0 OSPF 2

Within BGP, the locally generated route (10.2.1.38) is considered to be the best route. However, as shown in bold in the next example, the VRF routing table shows that the selected path is learned via OSPF with a next hop of 10.2.1.38, which is the Vienna CE router.

Cisco IOS Release 12.2(8)T

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