Document: draft-ietf-6lowpan-hc-13.txt
Reviewer: David L. Black
Review Date: January 17, 2011
IESG Telechat date: January 20, 2011

Summary: This draft is on the right track, but has open issues, described in
the review.

This draft is a complete redesign (in the form of new headers) of the IPv6
header compression support for IEEE 802.15.4 in order to make the result
usable in practice, and hence obsoletes the old formats.  The draft reflects
experience with the technology and contains a wealth of design details to
obtain as much leverage as possible from compression.  While I did not go
through all of the header details, the draft looks like it's in good shape and
the result of careful consideration.

I have one open issue.  The draft allows UDP checksums to be omitted when
there are higher level integrity checks in place, and says the following about
verification that those checks are in place:

   With this specification, a compressor in the source transport
   endpoint MAY elide the UDP checksum if it is authorized by the Upper
   Layer.  The compressor SHOULD NOT set the C bit unless it has
   received such authorization.

   ....

   A forwarding node MAY imply authorization from an incoming packet if
   the C bit is set.  A forwarding node that cannot unambiguously derive
   such authorization SHOULD NOT elide the UDP checksum when performing
   6LoWPAN compression.

Omission of UDP checksums has a lousy track record, suggesting that both of
the above should be "MUST NOT" instead of "SHOULD NOT".  There are plenty of
storage "war stories" about someone who ran NFS over UDP with checksums turned
off and later discovered corrupted files.

There may be something special about 802.15.4 that makes this sort of
corruption less of a risk, but I strongly request that the IESG discuss
whether to change both of the above "SHOULD NOT" statements to "MUST NOT" with
an explanation of the significant risks to data integrity (e.g., there's a
reason why RFC 2460 made the UDP checksum mandatory).

idnits 2.12.05 generated a few miscellaneous warnings, none of which require
changes to the draft.