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Subject: [Bug 217637] One TCP connection accepted TWO times
Date: Fri, 17 Mar 2017 07:03:11 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D217637

--- Comment #22 from Michael Tuexen <tuexen@freebsd.org> ---
(In reply to Sepherosa Ziehau from comment #21)
> Hmm, do any OS's TCP stacks really send data along w/ the last ACK in the
> 3-way handshake at all?
Assume the the initial ACK without data being the third message of the
handshake is
lost and the client will send data, like an HTTP client. Then the server wi=
ll
get
exactly such a packet. This will happen with most OSes, I guess.

> And if we are checking the syncookie, it indicates we suffered short-of-m=
emory
> previously.  I don't think we need to record that situation.
This is not true. We use the syncookie if we don't find an entry in the
syncache.
The reason can be that we had an overflow, but it can also be that we don't
find
it because we already used the entry to setup a connection. This is the code
path
we use in the traces provided.

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