Date: Sat, 31 Mar 2012 19:53:46 +1100 From: Darren Reed <darernr@freebsd.org> To: Jason Hellenthal <jhellenthal@dataix.net> Cc: freebsd-net@freebsd.org Subject: Re: FreeBSD TCP ignores zero window size Message-ID: <4F76C61A.1000704@freebsd.org> In-Reply-To: <20120330160055.GB78586@DataIX.net> References: <4F75C1A3.4030401@freebsd.org> <20120330160055.GB78586@DataIX.net>
next in thread | previous in thread | raw e-mail | index | archive | help
Jason Hellenthal wrote: > On Sat, Mar 31, 2012 at 01:22:27AM +1100, 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) >> >> In the packet flow below, 192.168.1.1 is FreeBSD and 10.1.1.1 >> is the other end. >> >> Darren >> > > Hi Darren, > > I do believe this is the following bug at first glance that was patched > after 8.2-RELEASE. and has to do more with x64 systems more than x32. > > See: "A Tale of a TCP Bug" for details... > > http://blogmal.42.org/tidbits/tcp-bug.story > > http://lists.freebsd.org/pipermail/freebsd-net/2011-April/028466.html > That patch alone is not enough to fix the problem - I still see FreeBSD 8.2 sending out data after it has received a TCP packet with a window size of 0. Next I'll try adding Andre's. Darren
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4F76C61A.1000704>