I have a deign issue that I have problem to solve.
Our customer has a mpls network and using different vpn's for different traffic types.
Between the two sites 10 ge links is used and intra 1 ge links is used.
OSPF is used in between GW, R1 and R2, (also between R1 and R2 to prevent GW to be transit )
During normal situations the traffic from Gateway to VRF A R2 goes via R2.
If the link B goes down the traffic should go via the other site, i.e GW to VRF 1 via R1 and R4.
That's is not the case because the ospf distance is better so it choose R1 => R2=> VRF A R2.
An idea I hade was to change ospf distance so it is higher then BGP.
After a test it works well during a faulty link (B).
However during normal operation (both link up)the traffic wil not use the right path i.e GW=>R1=>VRF-A R2.
Instead it will use GW=>R1=>R2=> VRF-A R2.
Why is this happend when I changing Distance?
Has somebody and idea how I can solve this?
the OSPF sham link is actually built by using BGP multiprotocol to carry specialized route targets that convey OSPF LSA information so that it can be rebuilt on remote PE.
In this way from the backbone point of view you are comparing MP BGP routes and this should help.
The sham link allows to rebuild O routes instead of O IA that is the normal type of rebuilded routes when using the MPLS superbackbone.
So seeing this from the customer side if you have a primary path that is O type and a secondary type that is O IA you should be fine.
Verify all fault and restore events to be sure that it works in any case.
It can be a possible solution.
Hope to help