[Lsr] Benjamin Kaduk's Discuss on draft-ietf-ospf-segment-routing-msd-21: (with DISCUSS and COMMENT)

Benjamin Kaduk <kaduk@mit.edu> Wed, 26 September 2018 22:02 UTC

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Date: Wed, 26 Sep 2018 15:02:00 -0700
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Subject: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-ospf-segment-routing-msd-21: (with DISCUSS and COMMENT)
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Benjamin Kaduk has entered the following ballot position for
draft-ietf-ospf-segment-routing-msd-21: Discuss

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This is essentially a process discuss, and hopefully easy to resolve.

In Section 4, we say:

   The meaning of the absence of both Node and Link MSD advertisements
   for a given MSD type is specific to the MSD type.  Generally it can
   only be inferred that the advertising node does not support
   advertisement of that MSD type.  However, in some cases the lack of
   advertisement might imply that the functionality associated with the
   MSD type is not supported.  The correct interpretation MUST be
   specified when an MSD type is defined.

I don't think we can make this sort of normative requirement on a registry
created by a different document, at least not without updating the registry
to also point to this document.


Can SID be expanded on first usage --
https://www.rfc-editor.org/materials/abbrev.expansion.txt does not list it
as "well known".  (It also doesn't appear to list "Segment Identifier" as
one of the expansions.)

This is basically the same thing I said for the IS-IS document that creates
the MSD types registry, but I'm not sure I followed correctly the meaning
of MSD type 1 for SR-enabled vs.  non-SR-enabled networks.  In particular,
I still don't really understand why it's okay to use the same codepoint for
the max SID depth in SR-enabled networks and for the max label depth in
non-SR MPLS networks.  Why couldn't they just be separate MSD Type

Section-by-section comments follow.

Section 2

                  If the Node MSD TLV appears in multiple Router
   Information LSAs that have the same flooding scope, the Node MSD TLV
   in the Router Information (RI) LSA with the numerically smallest
   Instance ID MUST be used and subsequent instances of the Node MSD TLV
   MUST be ignored. [...]

Unless there is a sorting requirement I've forgotten about, shouldn't this
be "other" rather than "subsequent"?

Section 6

Thanks for the updates in response to the secdir review; they help a lot.

   If the value is larger than supported - instantiation of a path that
   can't be supported by the head-end (the node performing the SID

This is supposed to mean "(instantiation by the head-end) of a (path that
can't be supported)", not "instantiation of a path (that can't be supported
by the head-end)", right?