Re: [Pce] Barry Leiba's No Objection on draft-ietf-pce-lsp-control-request-09: (with COMMENT)

Barry Leiba <> Mon, 30 September 2019 14:09 UTC

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From: Barry Leiba <>
Date: Mon, 30 Sep 2019 10:09:39 -0400
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To: Dhruv Dhody <>
Cc: The IESG <>,, Hariharan Ananthakrishnan <>, pce-chairs <>,
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Subject: Re: [Pce] Barry Leiba's No Objection on draft-ietf-pce-lsp-control-request-09: (with COMMENT)
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> > — Section 4 —
> >
> >    The D Flag and C
> >    Flag are mutually exclusive in PCUpd message.  The PCE SHOULD NOT
> >    send control request for LSP which is already delegated to the PCE,
> >    i.e. if the D Flag is set in the PCUpd message, then C Flag SHOULD
> >    NOT be set.
> >
> > I’m confused: “mutually exclusive” means that they can’t both be set.  So why
> > SHOULD NOT and not MUST NOT?  (You’re also missing a few articles here: ”a
> > PCUpd message”, “a control request”, “an LSP”, and “the C Flag”.
> >
> I think the reason for SHOULD NOT was because when a PCC receives this
> - it would simply ignore it!
> This did not rise to the level of error usual for MUST NOT!
> If you feel that the above isn't a good enough reason, changing would
> not cause any harm either.

If the working group thinks that SHOULD NOT is right, it should stay
that way -- I just questioned the combination of "mutually exclusive"
and "SHOULD NOT".  So here are my thoughts:

1. If there is no reason they should ever be set together, then it
should be MUST NOT.

2. If there might be a reason to set them together -- it's difficult
to meet the conditions in some way, or whatever -- then SHOULD NOT is

3. If you keep it as SHOULD NOT, I think you should change the
"mutually exclusive" sentence to be less strong.

It sounds to me like MUST NOT is the right thing here -- that there's
never a reason to set them both together, and that it doesn't make
sense in the protocol to have them both set.  So even though the
receiver can ignore the situation, MUST NOT still applies.