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
_______________________________________________
rtgwg mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/rtgwg
