IP identifier field for linux UDP/IP equals zero??!

davidn at rebel.net.au davidn at rebel.net.au
Thu May 15 08:22:57 CST 2003


Alan,

Alan Kennington <ak.linuxsa at topology.org> wrote:
> Concerning linux UDP/IP implementation, there seems to be a very
> inconvenient and incorrect choice for the "Identifier" field.
> 
> Every packet is supposed to have a different 16-bit Identifier field for
> a given src/dst pair of IP addresses for some period of time.
> However, I've just discovered that linux sends UDP/IP packets which
> have their DF (Don't Fragment) bit set with all identifier fields equal
> to zero!

My immediate thought on your question is this: Does the "some period of
time" have a defined minimum?

My second thought relates to the way in which UDP is used, which
can be connected but normally is connectionless.  TCP, of course,
is always connected, hence it's easy to increment a counter for each
packet w.r.t. any given src/dst pair.  That's nowhere near so easy for
a connectionless socket, and while it might be inconvenient, it also
might not be wrong (assuming the answer to my first question is "no")
to reset that counter for each connectionless UDP packet transmitted.

David

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