Hi:
Carsten asked for a crisper wording for which node can elide the UDP
checksum and when that happens. There seems to be a consensus that
we are not ready to open the door for heuristics based operations.
So at this point, only the source of a packet MAY elide the checksum,
And the receiver of a packet MAY ignore the checksum if it is present.
This in only allowed in the case of tunneling or stronger integrity
check above UDP.
Here is a proposed text:
"
With this specification, the source of a packet MAY elide the UDP
checksum in the following cases:
Tunneling: The source of the packet is tunneling another packet that
possesses its own integrity mechanism.
Upper Layer MIC: The Upper Layer Protocol over UDP uses an end-to-
end Message Integrity Check (MIC) that has stronger properties
than what is provided by the UDP checksum. Such an integrity
check MUST be end-to-end and cover the IPv6 pseudo-header, UDP
header, and UDP payload.
Only the source of a packet can know what Upper Layer operation takes
place. A router on the way that is not aware of such operation
SHOULD NOT elide the UDP checksum when performing 6LoWPAN
compression.
The 6LoWPAN termination point has to recompute the elided checksum
based on the received packet. If that point is a router, then the
router reforms a proper IPv6/UDP packet that can be forwarded on any
interface. If the 6LoWPAN termination point is the destination of
the packet and is aware of the presence of the Upper Layer MIC for
the destination UDP port, it MAY omit the UDP checksum operation
completely.
"
What do you think?
Pascal
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