Date: Sat, 31 Mar 2012 21:40:57 +1100 From: Darren Reed <darernr@freebsd.org> To: Andre Oppermann <andre@freebsd.org> Cc: freebsd-net@freebsd.org Subject: Re: FreeBSD TCP ignores zero window size Message-ID: <4F76DF39.7080807@freebsd.org> In-Reply-To: <4F76C929.5080400@freebsd.org> References: <4F75C1A3.4030401@freebsd.org> <4F75D9ED.7080707@freebsd.org> <4F76C929.5080400@freebsd.org>
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Darren Reed wrote: > Andre Oppermann wrote: >> On 30.03.2012 16:22, Darren Reed wrote: >>> I've been tracking down some problems with FreeBSD's sending >>> of TCP packets and seem to have come to the conclusion that >>> in FreeBSD 8.2-RELEASE, when the system is working with a >>> TCP connection that has a moderate delay in it, FreeBSD's >>> TCP ignores the other end telling it that the window size >>> is now 0 and continues to send data. I suspect that this is >>> meant to make sense because it is expecting that the ACK >>> that will open up the window is already in transit. But that >>> only accounts for the condition where the TCP on FreeBSD can >>> compute and decide that the remote TCP will have its buffer >>> full. What I find harder to accept is that when FreeBSD's >>> TCP receives a TCP packet from the remote end advertising >>> a window of 0, FreeBSD's response is to send more data and >>> not a window probe or is that now the expected behaviour? >>> And whilst you might say "ok" for a packet of data, I'm >>> somewhat hard pressed to explain why FreeBSD's TCP sends >>> multiple packets with data in them after receiving a TCP >>> packet from the other end advertising a zero window size. >>> >>> However this causes a problem with firewalls (;_) that are >>> close to the FreeBSD end because for them, it appears that >>> FreeBSD is sending data outside of its window. >>> >>> Is this a known problem? >>> If so, has it been fixed in a later version of FreeBSD? >>> (No, I haven't tested anything other than 8.2) >> >> The window update acceptance test is too restrictive. In your case >> the last updated seq# tracking gets it wrong and prevents the update. >> >> The code hasn't changed for a long time and newer versions behave the >> same. >> >> The concept patch below simplifies the logic, better tracks the seq# >> and is a bit more permissive. >> > > This patch does not apply cleanly against 8.2 (BYTES_THIS_ACK > is not present in 8.2.) > > I'll add in the obvious missing #defines and see how I go. This patch does not resolve the problem either. Darren
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