Last Call Review of draft-ietf-idr-bgp-ls-segment-routing-msd-16
review-ietf-idr-bgp-ls-segment-routing-msd-16-rtgdir-lc-chen-2020-04-17-00

Hello,

I have been selected as the Routing Directorate reviewer for this draft. The
Routing Directorate seeks to review all routing or routing-related drafts as
they pass through IETF last call and IESG review, and sometimes on special
request. The purpose of the review is to provide assistance to the Routing ADs.
For more information about the Routing Directorate, please see
​http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir

Although these comments are primarily for the use of the Routing ADs, it would
be helpful if you could consider them along with any other IETF Last Call
comments that you receive, and strive to resolve them through discussion or by
updating the draft.

Document: draft-ietf-idr-bgp-ls-segment-routing-msd-16.txt
Reviewer: Mach Chen
Review Date: April 17, 2020
IETF LC End Date:
Intended Status: Standards Track

Summary:
I have some minor concerns about this document that I think should be resolved
before publication.

Comments:
This document is clearly written and easy to understand.

Major Issues:
No major issues found.

Minor Issues:
The Node MSD TLV and Link MSD TLV are designed to be able to carry multiple
MSDs. I guess this is designed for future extensibility, where a Node may have
multiple types of MSD, right? But for each type, is it allowed to carry
multiple instances of MSD-Type/MSD-Value pair or only one instance? For
whichever case, there need some text to describe the rule about the sending and
receiving procedures. For example, when multiple instances allowed, how does a
node decide which instance takes effect; if only one instance allowed and
multiple instances received, how to handle this, discard the whole TLV, or only
the first instance takes effect and the rest ignored.

Nits:
1.
Section 1,
s/learn/learns

2.
Section 3 and Section 4:
The TLV format of Node/Link MSD is defined as follows:
      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    MSD-Type   |  MSD-Value    |  MSD-Type...  |  MSD-Value... |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Since the MSD-Type/MSD-Value pairs are variable in length, the above definition
does not reflect this, suggest to change the figure as below:
      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |             Length            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //    MSD-Type   |  MSD-Value    |  MSD-Type...  |  MSD-Value... //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Best regards,
Mach