Thanks for the comment
Regarding the paragraph from section 6 that you are referring to, this
paragraph was part of an example and not a recommendation.
RFC5286 and RFC7490 are referred to in
draft-ietf-rtgwg-segment-routing-ti-lfa. So IMO it would be redundant to
add any recommendation in draft-ietf-rtgwg-segment-routing-ti-lfa that
already exist in the RFCs.
Thanks
Ahmed
On 12/30/23 2:46 PM, Hemant Sharma wrote:
Hello,
The RFC 7490, 5.2.2. Selecting Repair Paths, provides a
recommendation on how to choose a PQ node when multiple options are
available.
such as,
"For consistency in behavior, it is RECOMMENDED that the member of the
set of routers {PQ} with the lowest cost S->P be the default choice
for P."
or
"As described in [RFC5286], always selecting a PQ node that is
downstream to the destination with respect to the repairing node
prevents the formation of loops when the failure is worse than
expected. The use of downstream nodes reduces the repair coverage,
and operators are advised to determine whether adequate coverage is
achieved before enabling this selection feature."
whereas, in the current draft, 6. TI-LFA Repair path, there is only a
subtle reference to the selection of a specific P node, as shown below
* P(S, N1) intersection with PCPath is [N2, R1], *R1 being the deeper
downstream node in PCP, it can be assumed to be used as P node*
(this is an example and an implementation could use a different
strategy to choose the P node).
However, in Section 6.2 on FRR path using a PQ node, there is no
explicit mention of the scenario when there are multiple PQ nodes
along the post-convergence path.
I believe it is worthwhile to include similar recommendations here for
the sake of completeness, either in the same section or creating
another one, copying this part from above.
"For consistency in behavior, it is RECOMMENDED that the member of the
set of routers {PQ} with the lowest cost S->P be the default choice
for P."
or
"As described in [RFC5286], always selecting a PQ node that is
downstream to the destination with respect to the repairing node
prevents the formation of loops when the failure is worse than
expected. The use of downstream nodes reduces the repair coverage,
and operators are advised to determine whether adequate coverage is
achieved before enabling this selection feature."
Please confirm if I have correctly understood this.
Thanks!
Regards,
Hemant Sharma
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