TCP zombie connections with 7-RELEASE and STABLE from 15th june

[Bernd Walter]

On Fri, Aug 01, 2008 at 12:08:38AM -0500, Mike Silbersack wrote:
> 
> 
> On Fri, 18 Jul 2008, Bernd Walter wrote:
> 
> >443 is a self written server, but it also happens with port 80 and
> >sslproxy.
> >The client is a telnet, which disconnects directly after connecting,
> >so the disconnect is initiated from the client, which seems to be
> >important for this problem to trigger.
> >
> >You can see that the FIN handshake completes and netstat on the
> >client box shows the connection in TIME_WAIT.
> >The server however has the connection still in ESTABLISHED state.
> 
> Well, syncookies allow the ack of the 3WHS to establish a connection. 
> Just a quick look at your tcpdump shows that since you aren't sending any 
> data you are not advancing the sequence number.  As a result, it looks 
> like one of the ACKs the client sends during connection shutdown may 
> actually be causing the server to re-establish the connection.

Ah - that makes sense.

> You might want to file a PR with exact instructions (and code) that'll 
> easily reproduce this so that it can be solved at some point in the 
> future.  I don't have time to look into it now, although I'd be happy to 
> code review a fix!

Thank you - I will file a PR.

-- 
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.