Re: I-D Action: draft-bashandy-rtgwg-segment-routing-ti-lfa-01.txt

["Ahmed Bashandy (bashandy)" <[e-mail]>]

See my reply to Sikhi

Thanks

Ahmed


On 8/7/2017 2:13 AM, Stewart Bryant wrote:
>
>
>
> 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
>
>
>
>