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
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tsv-art@ietf.org if you reply to or forward this review.

This document describes v4-via-v6 routing, and defines related operational
procedures, notably the origination of ICMPv4 packets by nodes that might
not have an IPv4 address. As such, it does not raise significant transport
concerns.

The section 4 mentions of path MTU discovery and packetization layer path
MTU discovery in connection with ICMPv4 look reasonable, although the
paragraph that contains them has some nits that need attention:

A router must therefore be able to generate ICMP Destination Unreachable messages
([RFC1812] Section 5.2.7.1). The source address of these messages must be one of the
addresses assigned to the outgoing interface; if no such address has been assigned,
then one of the other addresses assigned to the router, known as the "router-id",
must be used ([RFC1812] Section 4.3.2.4).

- I see three instances of "must" that ought to be "MUST" (or revised to use
a different word).

- In the first line, ICMP needs to be ICMPv4.  Given the importance of using
ICMPv4 and not ICMPv6, I suggest dropping the convention that in this document
ICMP means ICMPv4 and explicitly using ICMPv4 every time.

Much as I trust the authors (e.g., Warren) to get this right, the OPS area really
ought to do a a careful thorough review of section 6. Operational Considerations.