On Feb 19, 2008, at 12:22 PM, Noel Chiappa wrote:
> <Apologies that this ia a bit old, but it repeats a - sadly - very
> common
> misperception that is worth correcting yet again.>
>
>> From: Iljitsch van Beijnum <iljitsch@xxxxxxxxx>
>
>> If a protocol doesn't need port numbers or a UDP-like checksum (i.e.,
>> either no checksum or a better one)
>
> UDP does provide for packets with no checksum. Read the spec:
>
> "An all zero transmitted checksum value means that the transmitter
> generated no checksum (for debugging or for higher level
> protocols that
> don't care)."
>
Not AFAICT in IPv6 :
rfc2460 :
o Unlike IPv4, when UDP packets are originated by an IPv6 node,
the UDP checksum is not optional. That is, whenever
originating a UDP packet, an IPv6 node must compute a UDP
checksum over the packet and the pseudo-header, and, if that
computation yields a result of zero, it must be changed to hex
FFFF for placement in the UDP header. IPv6 receivers must
discard UDP packets containing a zero checksum, and should log
the error.
There has been discussion recently about relaxing this in UDP
tunnels, such as AMT.
Regards
Marshall
> (Minor pet peeve: we did blow it very microscopically, IMO; the
> reserved
> value should have been all ones, not all zeros, as all ones could
> never be a
> legitimate output from the checksum-generation step, but that's a
> minor
> quibble.)
>
> Noel
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