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OSPF
Feature Overview
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 86, type intra area
Redistributing via bgp 215
Advertised by bgp 215
Last update from 10.2.1.38 on Serial0/0/0, 00:00:17 ago
Routing Descriptor Blocks:
*10.2.1.38, from 10.3.1.7, 00:00:17 ago, via Serial0/0/0 Route metric is 86, traffic share count is 1
This path is selected because:
•The OSPF
•OSPF has a lower administrative distance (AD) than internal BGP (BGP running between routers in the same autonomous system).
If the backdoor links between sites are used only for backup purposes and do not participate in the VPN service, then the default route selection shown in the preceding example is not acceptable. To reestablish the desired path selection over the MPLS VPN backbone, you must create an additional OSPF
A
Figure 3 shows a sample sham-link between PE-1 and PE-2. A cost is configured with each sham-link and is used to decide whether traffic will be sent over the backdoor path or the sham-link path. When a sham-link is configured between PE routers, the PEs can populate the VRF routing table with the OSPF routes learned over the sham-link.
Cisco IOS Release 12.2(8)T
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