OSPF Sham Links

An OSPF Sham Link is a virtual point to point OSPF interface that’s formed over an MPLS backbone. The Sham Link can only be used between VPN sites that are part of the same OSPF domain. OSPF type 1 and 2 LSA’s are carried over the sham link using MP-BGP
To configure the sham link an additional loopback address is created to identify the end point of the link. The loopback is added to the VRF configuration and globally within the OSPF process to define the sham link local end point. The remote end point is configured within the OSPF are configuration with the other interfaces. A metric can also be added to the sham link.

interfaces {
     lo0.1 {
          family inet {
               address 172.25.1.1/32;
          }
     }
}
routing-instances {
     vpn-a {
          instance-type vrf;
          interface ge-0/0/0;
          interface lo0.1;
          route-distinguisher 172.25.0.1:1;
          vrf-target target:65001:100;
          protocols {
               ospf {
                    sham-link local 172.25.1.1;
                         area 0.0.0.0 {
                              sham-link remote 172.25.1.2 metric 10;
                              interface ge-0/0/0;
                         }
               }
          }
     }
}

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