sham-link question

[yuchenglai]

Hi All,

I have a question regarding sham-links. If I use a sham-link between two PE  routers, I know that a /32 address on the OSPF VRFs of the PEs must be  advertised via MP-BGP. 

However,  if the VRFs running OSPF on the two PE routers want to learn about one another's OSPF  routes via the Sham-Link, can I assume that there is no need to  redistribute the OSPF into MP-BGP on the two PE routers?

David

[Marwan ALshawi]

you still need the redistribution for routing/forwarding over the core

the shame-link is spcial tunnel like virtual-link connect to PEs in same area and is used to establish

OSPF adjacency and LSA exchange

the LSA loaded to the OSPF Database and the intra-area route used over the sham-link for computing the path

HOWEVER, when the route being installed in a VRF's RIB the forwarding will be based on the MP-BGP learned routes based on prefix-match

the relevant VPN and lable then used for the packet forwarding over the MPLS core

so the info loaded across the Sham-link used for OSPF SPF calculations and best path selection

while the forwarding done via the info learned through MP-BGP

HTH

if helpful Rate

[yuchenglai]

That was very helpful, thanks.

I think you summed it up for me with your last statement:

"so the info loaded across the Sham-link used for OSPF SPF calculations and best path selection

while the forwarding done via the info learned through MP-BGP"

[Marwan ALshawi]

Happy to help

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