Early Review of draft-ietf-rtgwg-segment-routing-ti-lfa-11
review-ietf-rtgwg-segment-routing-ti-lfa-11-intdir-early-fressancourt-2023-07-18-00

I am an assigned INT directorate (early) reviewer for
draft-ietf-rtgwg-segment-routing-ti-lfa-09.txt. These comments were written
primarily for the benefit of the Internet Area Directors. Document editors and
shepherd(s) should treat these comments just like they would treat comments
from any other IETF contributors and resolve them along with any other Last
Call comments that have been received. For more details on the INT Directorate,
see https://datatracker.ietf.org/group/intdir/about/
<https://datatracker.ietf.org/group/intdir/about/>.

Based on my review, if I was on the IESG I would ballot this document as NO
OBJECTION.

The document is well written, and clear for a reader who has previous knowledge
of both Segment Routing and Fast Rerouting mechanism, which is my case. Yet, I
have some remarks to do on the document.

In section 6, you present the scheme of an example network that you use to
present TI-LFA Repair path. In the explanation you give about finding the P and
Q spaces, I think the reader would benefit from a picture showing the shortest
path tree from S and the reverse shortest path tree to D to better understand
why P and Q are as stated (in particular for P(S, N1) since R1 is not a direct
neighbor of S).

In section 7, the several cases that a PLR will face while building the TI-LFA
repair segment list are presented, but this presentation would benefit from
examples of topologies and before / after segment lists that would help the
reader get the principle of the building method suggested by the document.

In section 12, while I highly appreciate the effort made by the authors to
present measurements about the potential benefit of TI-LFA, I felt (a bit)
frustrated by the fact that the topologies are presented but not made available
for the reader to look at them in details and to assess the results presented
in the document against a potential implementation he would make. I know that
publishing such topologies is difficult, so I would suggest that at least one
or two publicly available topologies (for instance from the Internet Topology
Zoo (http://www.topology-zoo.org/) or from the Defo dataset
(https://sites.uclouvain.be/defo/)) are investigated so a motivated and curious
reader could try for him/herself.