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SubjectRe: ack number in a connection-refused RST
On Fri, Oct 06, 2000 at 09:06:31PM +0000, David Wagner wrote:
> David S. Miller wrote:
> >Linux should not honor the incorrect sequence number. If the sequence
> >number is incorrect, the RST could legitimately be for another
> >connection.
>
> How could it be for another connection, if it has source and destination
> port numbers? I thought the sequence number was there to prevent denial
> of service attacks, i.e., to prevent unauthorized third parties from
> tearing down established TCP connections; since third parties will not
> know (or be able to guess) the current 32-bit sequence number, they will
> be unable to forge a valid RST packet. Of course, this argument is still
> valid even if you accept off-by-one errors in the sequence number; the
> attacker still has to guess from a 31-bit space, which is slightly smaller
> than the original 32-bit space but still likely large enough for security.
> What am I missing?

You're missing dynamic IPs, NAT and reboot of hosts.


-Andi
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