[e2e] ICMP & TCP segments with IP ID = 0?
Craig Partridge
craig at aland.bbn.com
Wed May 16 09:24:11 PDT 2001
In message <20010516111231.A16714 at host-186.dyn.dev.zks.net>, Jerome Etienne wri
tes:
>what is so evil in setting the IPv4 id to 0, assuming the DF bit is set ?
I said it was "evil" because it is not in compliance with the specifications
(namely RFC791 and 1122).
Interestingly enough, while RFC 1122 certainly assumes that a new identifier is
normally required for each datagram, it doesn't say so.
But RFC 791 is quite clear:
The originating protocol module of
an internet datagram sets the identification field to a value that
must be unique for that source-destination pair and protocol for the
time the datagram will be active in the internet system.
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).
Craig
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