On Nov 19, 2008, at 07:39 , Shoichi Sakane wrote:
Hi Carsten,
What I was talking about UDP-NAT is only about the recalculation
of the UDP checksum. I didn't mean the address translation happened
with this 6lowpan case.
OK.
(I still think it's worth to make the point that the ULTP MIC renders
legacy NATs unusable unless there is a way to undo the damage before
checking/generating the MIC.)
I don't understand why the 6lowpan stack of the receiver builds the
UDP
checksum after the ULTP stack has checked the ULTP MIC ?
It shouldn't (unless the implementation is so cleanly layered that the
UDP layer would immediately discard the packet). Did I say that?
At the compressor, you *have* to layer-violate, as usual.
It is straightforward
that the UDP checksum is built by the 6lowpan stack before the UDP
stack gets
the decompressed message before the ULTP stack will get the message.
Again, if your implementation is that cleanly layered.
Conceptually speaking, you are right.
I am thinking that all of the decompressing is processed at the
6lowpan stack
which is dedicated under the IP stack. Am I misunderstanding ?
No, conceptually, you are right.
But when you argue about complexity of implementation, in reality
there will be a signal from the decompressor that the UDP layer does
not have to bother checking (actually, that the whole UDP layer is
bypassed except for port numbers).
Gruesse, Carsten
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