[babel] Martin Duke's No Objection on draft-ietf-babel-yang-model-10: (with COMMENT)

[Martin Duke via Datatracker <[e-mail]>]

Martin Duke has entered the following ballot position for
draft-ietf-babel-yang-model-10: No Objection

When responding, please keep the subject line intact and reply to all
email addresses included in the To and CC lines. (Feel free to cut this
introductory paragraph, however.)


Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
for more information about DISCUSS and COMMENT positions.


The document, along with other ballot positions, can be found here:
https://datatracker.ietf.org/doc/draft-ietf-babel-yang-model/



----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

(2.3)

leaf received-metric {
           type uint16;
           description
             "The metric with which this route was advertised by the
              neighbor, or maximum value (infinity) to indicate the
              route was recently retracted and is temporarily
              unreachable. This metric will be 0 (zero) if the route
              was not received from a neighbor but was generated
              through other means. At least one of
              calculated-metric or received-metric MUST be non-NULL.";
           reference
             "RFC ZZZZ: Babel Information Model, Section 3.6,
              RFC 8966: The Babel Routing Protocol, Section 2.1.";
         }

         leaf calculated-metric {
           type uint16;
           description
             "A calculated metric for this route. How the metric is
              calculated is implementation-specific. Maximum value
              (infinity) indicates the route was recently retracted
              and is temporarily unreachable. At least one of
              calculated-metric or received-metric MUST be non-NULL.";
           reference
             "RFC ZZZZ: Babel Information Model, Section 3.6,
              RFC 8966: The Babel Routing Protocol, Section 2.1.";
         }

I don't understand the relationship between these two. If the metric was
calculated rather than received, why would the value be zero instead of NULL?
Isn't a zero metric dangerous in a routing algorithm?

(4) "config true perspective"?