Re: ack number in a connection-refused RST

From: David Wagner (daw@mozart.cs.berkeley.edu)
Date: Fri Oct 06 2000 - 17:34:35 EDT

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    Andi Kleen wrote:
    >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?
    >
    >You're missing dynamic IPs, NAT and reboot of hosts.

    Ok, but with dynamic IP, NAT, and reboots, you can also get incorrect
    results with today's implementation, if you see a RST with the correct
    sequence number (not the off-by-one incorrect one). It's just a
    probabilistic argument that this is unlikely to happen in practice --
    namely, it only happens with probability 1/2^32 (you hope).

    There's no fundamental reason why you couldn't accept off-by-one sequence
    numbers as well, if it was deemed important for interoperability;
    the probability would just increase to 1/2^31, which is still small
    (albeit not as small as 1/2^32).

    Right? Or am I still missing something? I'm not a TCP expert.
    -
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