RE: Request for RTGWG Working Group adoption for draft-bashandy-rtgwg-segment-routing-ti-lfa

<> Fri, 13 July 2018 12:37 UTC

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To: Stewart Bryant <>, Alexander Vainshtein <>, DECRAENE Bruno IMT/OLN <>
CC: Robert Raszuk <>, "" <>, "" <>, "" <>, "" <>, "" <>
Subject: RE: Request for RTGWG Working Group adoption for draft-bashandy-rtgwg-segment-routing-ti-lfa
Thread-Topic: Request for RTGWG Working Group adoption for draft-bashandy-rtgwg-segment-routing-ti-lfa
Date: Fri, 13 Jul 2018 12:37:48 +0000
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Hi Stewart,

TILFA is not intended to provide a loop free path at all phases of the convergence process. As any FRR technique (or most), it may suffer from micro-looping when the PLR has converged and rewrites the path out of the computed FRR path.
TILFA just encodes the postconvergence path seen from the PLR point of view in a loop free manner and the resulting label stack is used only during the FRR.

Global microloop avoidance is also doable using similar mechanism as TILFA, but that’s another story.
RFC8333 (local delay) can also be used in conjunction with TILFA to protect against local microloops that are caused by a link down.

From: Stewart Bryant []
Sent: Thursday, July 12, 2018 15:47
To: LITKOWSKI Stephane OBS/OINIS; Alexander Vainshtein; DECRAENE Bruno IMT/OLN
Cc: Robert Raszuk;;;;;
Subject: Re: Request for RTGWG Working Group adoption for draft-bashandy-rtgwg-segment-routing-ti-lfa

On 12/07/2018 13:47,<> wrote:
TILFA helps here as it can use a loopfree IGP metric optimized path

All IPFRR paths are loop free against the number of failures that they set out to guard against.

However not all techniques are loop-free at all phases of convergence, and you now recognize that to be the case with this method.

Some methods are unconditionally stable against any degree of failure (down stream repair), although this is achieved at a cost of reduced coverage. All other methods are potentially looping and need a method of retrieving the situation which I did not see documented in this draft.

- Stewart


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