--> OSPF Sham link is used when there is a backdoor link between two customer sites and MPLS VPN Connectivity.
--> The problem with this scenario is CE routers will prefer path via back door compared to MPLS VPN Connection because of OSPF best path selection algorithm ( Intra Area vs Inter Area).
--> The concept of Sham link introduced to solve this problem.
--> The Sham link is a logical link ( Intra Area Link ) created between two PE routers.
--> All the OSPF LSA types are preserved which are going via PE routers and they are not converted to LSA type 3 and LSA type 5.
--> Once Sham link is created then the customer sites will communicate each other via MPLS backbone.
--> So the basic concept of the sham link is to make Inter Area Routes/External Routes as Intra Area Routes.
Md.Kareem
CCIE # 54759
--> The problem with this scenario is CE routers will prefer path via back door compared to MPLS VPN Connection because of OSPF best path selection algorithm ( Intra Area vs Inter Area).
--> The concept of Sham link introduced to solve this problem.
--> The Sham link is a logical link ( Intra Area Link ) created between two PE routers.
--> All the OSPF LSA types are preserved which are going via PE routers and they are not converted to LSA type 3 and LSA type 5.
--> Once Sham link is created then the customer sites will communicate each other via MPLS backbone.
--> So the basic concept of the sham link is to make Inter Area Routes/External Routes as Intra Area Routes.
Md.Kareem
CCIE # 54759
but why it will choose sham link over backdoor link as both links are intra-area links ?
ReplyDeleteWe have to make sure cost of the sham link should be less than backdoor link
Deleteohh yes got it. thanks.. :)
Delete