Re: [Last-Call] [Tsv-art] [lp-wan] Tsvart last call review of draft-ietf-lpwan-coap-static-context-hc-12

[Joseph Touch <touch@xxxxxxxxxxxxxx>]

On Mar 17, 2020, at 4:30 PM, dominique.barthel@xxxxxxxxxx wrote:

This "if properly implemented" seems pretty critical.  Do we need to leave
a reminder that implementations have to know about UDP TLVs in order to
properly identify all fields in the headers to be compressed?

Indeed, the protocol parser and the SCHC rules need to know about the UDP
TLVs if one wants to compress them.
But the same is true of all the other fields. I don't think this one
warrants a special notice.
What I insist on is that, if an implementation does not know of the UDP
TLVs, it will not reconstruct an erroneous UDP Length, even for a packet
that contains these TLVs, assuming that the protocol parser checks the UDP
and IPv6 lengths for consistency. See my example in a separate mail.

Agreed. The issue is that UDP length can’t be reconstructed UNLESS it matches the end of packet indicated by the IP length.

In any other case, claiming it can be reconstructed is an error and should not be allowed.

That appears to be a flaw in the claim that UDP length can be computed. It’s just not true in all cases.

Joe

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