Hi all,
Please see below the comments I planned to present during the discussion at the
RTGWG session today:
1. TI-LFA draft is about local handling of failures, while the micro-loop
avoidance one is not limited to local reaction and deals with any kind of
topology changes, including (but not limited to) recovery of failed
links/nodes. Therefore, I do not think that merging these two drafts is a good
idea.
2. At the same time, I fully agree that relationship between TI-LFA and
micro-loop avoidance should be clarified, preferably in the updated TI-LFA
draft. The current (-11) revision:
* The term micro-loop (sometimes spelled as "microloop") does not appear
at all in the text
* There is what I looks to me as a vague hint to micro-loop avoidance in
Section 6 of the TI-LFA draft that says (the relevant text is highlighted):
"The repair list encodes the explicit post-convergence path to the destination,
which avoids the protected resource X and, at the same time, is guaranteed to
be loop-free irrespective of the state of FIBs along the nodes belonging to the
explicit path". This statement:
i. Is
obviously correct
ii. May be
perceived as referring to TI-LFA paths represented by explicit lists of Adj-SIDs
iii. Seems to
ignore the fact that TI-LFA paths computed in accordance with the definitions
in Section 6.1, 6.2, 6.3 and, presumably, 6.4 of the draft would not be
affected the state of the FIBs long the nodes they cross regardless of matching
the post-convergence path constraint. This fact is not mentioned anywhere in
the TI-LFA draft
* I have proposed (on the list) tentative text clarifying this
relationship, and suggested placing it in a dedicated section of the draft.
1. Section 2 of the TI-LFA draft states that the benefit of the repair paths
following post-convergence paths from the PLR (but not from the ingress node)
to the destination is reduction of the "need for locally configured policies
that drive the backup path selection". However, it does not update RFC
7916<https://www.rfc-editor.org/rfc/rfc7916.html> that defines the ways to
specify such policies.
* To me this suggests that congruence of the repair and post-convergence
path is not mandatory
* In any case it would be nice to clarify all the benefits associated
with usage of the post-convergence paths, possibly in a dedicated section of
the draft.
Hopefully, these comments will be useful.
Regards,
Sasha
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