MPLS provides the flexibility to link VPN sites in a number of ways. When several VPNs get access to a shared part of network infrastructure, this is called an extranet .
Below Topology show the example of MPLS Traffic Engineering VPN with Extranet.
Attach link is the complete document for same
http://chetanress.blogspot.com/2010/08/mpls-traffic-engineering-vpn-with_10.html
Regards
Chetan Kumar Ress