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Routing & Switching · Advanced

OSPF Sham Link

A logical intra-area link between PEs across the MPLS backbone so VPN routes are preferred over an OSPF backdoor link.

Definition

Without a sham link, routes via the MPLS VPN appear inter-area while a backdoor link carries intra-area routes, which always win. The sham link makes the MPLS path intra-area so cost decides.

Example

area 0 sham-link 10.1.1.1 10.2.2.2 cost 10 under router ospf 10 vrf CUST

Exam tip

Sham link endpoints are /32 addresses in the VRF advertised via BGP, not OSPF.

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