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SubjectRe: help on fin_wait
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"Matts Kallioniemi" <matts@mejl.com> writes:

>
> > NO NO NO
> >
> > The TCP time wait period is defined by the RFC and constrained
> > by internet and mathematical requirements neccessary to handle
> > a non infinite sequence space - ie a safety time before reuse.
> >
> > Anyone who lowers that is not talking TCP and risks ack fights
> > and data corruption.
> >
> > Alan
>
> Then what action do you recommend for somebody who is trying to restart their crashed server? If one rebooted the machine within fifteen minutes, would that comply with the RFC?

Linux circumvents the problem by using a MD5/SHA hash of
(secret from random device, saddr, daddr, sport, dport,
timestamp from realtime clock) to initialise the sequence numbers of new
connections. That first makes TCP spoofing a lot more difficult and also
has the nice effect of making sequence space collisions after crashes very
unlikely.


-A.

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