Hello @pradyumnayadavgla
It seems that you posted this in a private message. I will quote it here, and respond to it so that all of our readers can benefit.
Hi Rene,
Q1- Sham link can only be used for CE-PE OSPF not with other IGP like EIGRP and RIP?
Q2- can it is possible to use sham link when we are using OSPF for CE-PE connectivity
and other IGP using for providing reachability b/w IBGP neighbors or vice versa?
Q3- Did not understand concept of MPLS VPN backbone mean which link will act as
MPLS VPN backbone and if sham link is the MPLS VPN backbone link mean we are
having primary and sec MPLS VPN link and total two backbone link for each
customers
Q1 A sham link is an OSPF concept and cannot be implemented using other routing protocols.
Q2 A sham link can only be created when OSPF is the IGP in the MPLS backbone. If you are running EIGRP between the CE and PE, then a sham link, although it can be created, is of no benefit, because the redistribution between OSPF and EIGRP takes place in the PE, and there, you can adjust the metric of the EIGRP routes to achieve what you would with the sham link. Remember, the sham link is there because OSPF will always prefer an intra-area route (O) over an inter area route (O IA). The sham link simply changes the categorization of the O IA route to an O route so that it can be preferred. EIGRP doesn’t have such a concept, so it is not necessary.
Q3 The “VPN Backbone” is simply the MPLS network composed of the PE and P routers. The sham link isn’t the backbone, it is simply a mechanism that changes the categorization of the actual OSPF route. It’s not a tunnel of any sort, nor a backbone. The backbone is the MPLS network itself.
I hope this has been helpful!
Laz