I am an assigned INT directorate reviewer for draft-ietf-babel-rtt-extension in version 05. These comments were written primarily for the benefit of the Internet Area Directors. Document editors and shepherd(s) should treat these comments just like they would treat comments from any other IETF contributors and resolve them along with any other Last Call comments that have been received. For more details on the INT Directorate, see https://datatracker.ietf.org/group/intdir/about/ <https://datatracker.ietf.org/group/intdir/about/>.

Based on my review, if I was on the IESG I would ballot this document as YES.

The text of the draft is clearly written, and easy to follow. To the best of my understanding, the metric, sub-TLVs and mechanisms described in the draft are consistent with RFC 8966, in particular with the considerations for protocol extensions in Appendix D.

The following are minor issues (typos, misspelling, minor text improvements) with the document:

* In some parts of the draft, the authors personalize their text using "we" or "our" (for instance in section 3.3 or in the introduction of section 4). The authors might want to rephrase those sentences using a more neutral form.

* In section 4.1, I was frustrated by the use of vague terms like "fairly" or "somewhat" which gives the impression that the phenomenon described is difficult to observe, and may not require the use of a proper smoothing algorithm.

* In section 4.1 and 4.3, the text mentions external references to describe algorithms that the implementer could be using to avoid strong oscillations in the route selection algorithm. I would have appreciated to have a rough intuition of the behavior of those algorithms in the text directly, while keeping the reference to point to more detailed descriptions.