Consider the below topology from RFC 3906 and all ospf link cost as 10 and two TE-tunnels T1: (RTA-RTD) and T2: (RTA to RTE via rtrC)
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rtrD -- rtrE
In OSPF, after calcualting SPT till rtrB, suppose we choose rtrD from candidate list to put into SPT, we first modify rtrD routers nexthop to T1 with cost 1 which is a fixed cost assigned to all TE-Tunnel by MPLS in my algorthim.Then we choose rtrE(cost 11, compare to rtrC with cost 20) from candidate list and modify the nexthop to T2 with cost of 1.
Now, to reach rtrC, the cost from rtrE to rtrC is 11 because of TE-tunnel T2, while from rtrB is 20, hence we modify rtrC's nexthop to TE tunnel T2.
This is wrong as all traffic going to rtrC, will go to rtrE via tunnel T2 (via rtrC), then routed back to rtrC.
i though of checking with the help of mpls, while modifying nexthop of rtrC to tunnel T2, whether any of RTC's address is present in nexthop list of TE Tunnel T2, basically avoiding a loop, but in some cases mpls will not have nexthop list(no RROs), hence stuck ?
so can anyone think of any other solutions ?
Regards
Santosh