[Lsr] Yangdoctors last call review of draft-ietf-lsr-yang-isis-reverse-metric-01

Ladislav Lhotka via Datatracker <noreply@ietf.org> Wed, 16 December 2020 12:12 UTC

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Subject: [Lsr] Yangdoctors last call review of draft-ietf-lsr-yang-isis-reverse-metric-01
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Reviewer: Ladislav Lhotka
Review result: Ready with Issues

**** General comments

- YANG module "ietf-isis-reverse-metric" is in a good shape except for
  one issue described below.
- I appreciate the three examples of instance data in appendices (two
  in XML representation, one in JSON).

**** Specific comments

- In three places, the module uses "when" expressions with plain
  string equality test applied to identityref values, such as:

     when "../rt:type = 'isis:isis'"

  This is known to be fragile, which can demonstrated on the JSON
  example in appendix A.3: It has

     "type": "ietf-isis:isis"

  which makes the "when" expression false because of the different
  prefix, and the corresponding augment doesn't happen.

  The above "when" expression should use the XPath function
  "derived-from-or-self" that is defined in RFC 7950:

     when "derived-from-or-self(../rt:type, 'isis:isis')"  
- The "tlv16-reverse-metric" grouping is used only once in the
  module. Unless it is expected to be used elsewhere, I would
  recommend to remove this grouping and use its contents directly.

- The phrase "YANG XML data" is somewhat misleading, although it is
  probably often used in informal discussions. I would suggest "XML
  instance data" instead.

**** Nits

- Abstract & Introduction: s/routeing/routing/

- Appending A.3: s/YANG XML data/JSON instance data/