area sham-link

Use this command to configure an OSPF sham link between two PE routers.


area area-id sham-link source-ipv6-address destination-ipv6-address
no area area-id sham-link source-ipv6-address destination-ipv6-address


area-id Specifies the OSPF area the two PE routers belong to.
source-ipv6-address Specifies the source IPv6 address for this sham link.
destination-ipv6-address Specifies the destination IPv6 address for this sham link.


If no sham link option is specified, the following defaults are used:

  • authentication key - none
  • dead-interval - 60 seconds
  • hello-interval - 10 seconds
  • keychain - none
  • message-digest-key - none
  • retransmit-delay - 5 seconds
  • cost - reference bandwidth divided by the interface bandwidth


VRF configuration, OSPF router configuration.


If a VRF contains both an OSPF-distributed route and a VPN-IPv4 route for the same IPv4 prefix, then the backdoor OSPF-distributed route is preferred over the VPN backbone route, unless the next hop interface for an installed (OSPF distributed) route is the sham link, in which case, the VPN backbone VPN-IPv4 route is used.

If it is desired to have OSPF prefer the routes through the VPN backbone over the routes through the OSPF backdoor link, then the routes through the backbone must appear to be intra-area routes. The sham link provides this appearance of an intra-area link connecting the two PE routers.

The “no” form of this command deletes the configured sham link.


This example shows how to configure a sham link between two PE routers with a source address of 2001:FA04:0005:0001::0 and a destination address of 2002:FA04:0005:0002::0 on OSPF router instance 10, VRF doc:

System(su)->router doc
System(su-doc-config)->ipv6 router ospf 10
System(su-doc-config-ospf-10)->area 10 sham-link 2001:FA04:0005:0001::0 2002:FA04:0005:0002::0