[Lsr] Benjamin Kaduk's No Objection on draft-ietf-isis-segment-routing-msd-17: (with COMMENT)

Benjamin Kaduk <kaduk@mit.edu> Wed, 26 September 2018 21:46 UTC

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Date: Wed, 26 Sep 2018 14:46:15 -0700
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Subject: [Lsr] Benjamin Kaduk's No Objection on draft-ietf-isis-segment-routing-msd-17: (with COMMENT)
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Benjamin Kaduk has entered the following ballot position for
draft-ietf-isis-segment-routing-msd-17: No Objection

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COMMENT:
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The shepherd writeup is silent about the WG's discussion of the IPR
disclosure (but the corresponding ospf draft says this sort of thing is
typical for LSR drafts).

Section 3

   The link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and
   223 to carry the MSD of the interface associated with the link.  MSD

Please add the appropriate qualifier (IS-IS?) before the list of TLV
numbers.

   MSD-Value is a number in the range of 0-255.  For all MSD-Types, 0
   represents lack of the ability to support SID stack of any depth; any
   other value represents that of the link.

It's unclear that there's a referent for "that of the link" to attach to.
That is, is it better to say "represents the maximum SID depth supported by
the link" (or similar)?

Section 6

As discussed in the secdir review, this section needs to include guidance
to the Experts to check that the meaning of the absence of an MSD type is
specified.  Given the text in draft-ietf-ospf-segment-routing-msd that
attempts to place a similar requirement on future MSD types (but for OSPF
vs. IS-IS usage thereof), hopefully this guidance can be phrased in an
appropriately general fashion so as to apply to all places where the
registered MSD value would be used.

Section 7

   Advertisement of the additional information defined in this document
   that is false, e.g., an MSD that is incorrect, may result in a path
   computation failing, having a service unavailable, or calculation of
   a path that cannot be supported by the head-end (the node performing
   the imposition).

In the analogous OSPF document we split out the case of a value that is too
small and a value that is too large, to describe the different
consequences.

I would also suggest rewording to something like "calculation by the
head-end of a path that cannot be supported" to avoid the mis-parsing
"(calculation of a path) (that cannot be supported by the head-end)".