On 07/08/2017 06:45, Sikhivahan Gundu wrote:
By “ambiguity”, I meant that backup calculation taking SRLG into account is based on speculated topology, whereas computation of post-convergence path, ie, SPF, is based on actual topology. This seems needs reconciling since in TI-LFA the backup is by definition the post-convergence path, with a single path-transition after link-failure as the intended outcome. Do I understand correctly that the draft prefers to relax that expectation for SRLG?
Yes, that is a good point, in the event of an incomplete failure of an SRLG, there may not be congruence between the FRR path and the post convergence path. This certainly needs further study. * A--------//---------B | | | * | cost 2 C-------------------D | | | | cost 100 E-------------------F AB + CD in same SRLG TiLFA path is ACEFDB Post convergence path is ACDB In this case I think that the impact is just more SR hops in the repair path than might be needed without the SRLG, but we do need to be sure that there are no pathological cases in topologies that lack the proposed congruence, and as Sikhivahan notes this effect does need to be clarified in the text. - Stewart
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