![](/images/new-backgrounds/1106489/1064895x1.webp)
OSPF
Feature Overview
Figure 2 Backdoor Paths Between OSPF Client Sites
MPLS VPN Backbone
10.3.1.2
10.3.1.6PE-2
10.3.1.5
Winchester
10.3.1.7Area 1
Brighton
70391
Area 1 | Vienna | Stockholm | Area 1 |
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| 10.3.1.15 | 10.3.1.3 |
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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# 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
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
3