[Pce] Backward compatibility with earlier version of draft-ietf-pce-segment-routing

[Dhruv Dhody <[e-mail]>]

Hi WG,

To accommodate earlier implementations of PCEP-SR (before the path
setup type capability exchange was changed), we added this text to
allow backward compatibility with older versions -

   https://tools.ietf.org/html/draft-ietf-pce-segment-routing-14#section-7

   Some implementations, which are compliant with an earlier version of
   this specification, do not send the PATH-SETUP-TYPE-CAPABILITY TLV in
   their OPEN objects.  Instead, to indicate that they support SR, these
   implementations include the SR-CAPABILITY-TLV as a top-level TLV in
   the OPEN object.  Unfortunately, some of these implementations made
   it into the field before this document was published in its final
   form.  Therefore, if a PCEP speaker receives an OPEN object in which
   the SR-CAPABILITY-TLV appears as a top-level TLV, then it MUST
   interpret this as though the sender had sent a PATH-SETUP-TYPE-
   CAPABILITY TLV with a PST list of (0, 1) (that is, both RSVP-TE and
   SR-TE PSTs are supported) and with the SR-CAPABILITY-TLV as a sub-
   TLV.  If a PCEP speaker receives an OPEN object in which both the SR-
   CAPABILITY-TLV and PATH-SETUP-TYPE-CAPABILITY TLV appear as top-level
   TLVs, then it MUST ignore the top-level SR-CAPABILITY-TLV and process
   only the PATH-SETUP-TYPE-CAPABILITY TLV.

It has been a while since RFC8408 was published and this document
updated, and you might have already updated your implementations to
the latest standard.

- Are there any older implementations, still in the field that needs
to inter-operate with other pcep speakers that are running the latest
standard?
- If yes, can they be patched to latest standard in a planned manner,
without impacting the network operations?
- Please shout out the impact if the above text is removed.
- Further, if you have a valid rationale to keep the text, would you
be fine with changing MUST to SHOULD in the text?

Please respond by 8th Feb. You may choose to reply directly to the
chairs/AD instead of mailing list if you wish.

Thanks!
Dhruv (for the PCE chairs)