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Re: I-D Action:draft-rosenberg-internet-waist-hourglass-00.txt]

2008-02-19 12:35:31

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(_at_)muada(_dot_)com>

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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