IETF Last Call Review of draft-ietf-v6ops-framework-md-ipv6only-underlay-23
review-ietf-v6ops-framework-md-ipv6only-underlay-23-tsvart-lc-trammell-2026-06-22-00

This document has been reviewed as part of the transport area review team's
ongoing effort to review key IETF documents. These comments were written
primarily for the transport area directors, but are copied to the document's
authors and WG to allow them to address any issues raised and also to the IETF
discussion list for information.

When done at the time of IETF Last Call, the authors should consider this
review as part of the last-call comments they receive. Please always CC
tsv-art@ietf.org if you reply to or forward this review.

This document defines a stateless translation framework for using v6only
underlays in interprovider networks.

From a transport PoV, it's mostly ready, but I did have two concerns.

The approach relies on RFC 7915 for its packet translation (and therefore most
of the transport-relevant) behavior. It took me a while to understand how this
system would interact with ECN. While it's not *necessary* for this document to
state this explicitly (that 7915 supports ECN implicitly through "ToS byte"
copy, though with troubling guidance to allow administrative bleaching during
the translation process that I suspect has had and will continue to have
negative impact on ECN deployment), this was the first rabbithole I had to dig
into in this review.

More troubling is that fact that MTU issues are relegated to a paragraph in
operational concerns. Is this sufficient? The envisioned framework will see
multiple underlay hops, i.e. multiple MTU breaks, each with an MTU penalty. I'd
like to see an expanded treatment of this issue, given that I suspect it
represents the most serious challenge to the deployability of this framework.

Thanks, cheers,

Brian (tsv-art hat)