[e2e] ICMP & TCP segments with IP ID = 0?

Francesco Potorti` F.Potorti at cnuce.cnr.it
Wed May 16 10:20:50 PDT 2001

   I said it was "evil" because it is not in compliance with the specifications
   (namely RFC791 and 1122).

rfc 791 explicitely permits it, by saying that there are 65536 values.

And  I found  no  place in  either  791 or  1122  where an  id  of 0  is
prohibited or  even mentioned.   I may  have missed it,  but I  would be
grateful if someone game me a pointer.
   Interestingly enough, while RFC 1122 certainly assumes that a new
   identifier is normally required for each datagram, it doesn't say so.
In fact, I'd say that it does not make that assumption in the case when
DF is set.  But this is a different story.

   So while 0 is a valid value, you can't repeat it for the lifetime of
   a datagram or so (RFC 1122 permits reuse in the narrow case of
   retransmitting exactly the same data).

In fact, you necessarily end up reusing it for a connection on a big
enough pipe.

Francesco Potortì (researcher)         Voice: +39 050 315 3058 (op.2111)
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