One of my reader asked a question,"Normally customers require sham link to prefer back door link in case of MPLS VPN environment, when customer run same area. But if the customer is using different area, how the back door link work."
If we read RFC 2328 which is clearly states that to make communication possible between two areas,OSPF must have area 0 connectivity. In this type of topology, the backdoor will never work.
If someone is having any different thought, please share it.