Date: Sun, 7 Mar 2010 15:56:55 -1000 From: David Cornejo <dave@dogwood.com> To: Chuck Swiger <cswiger@mac.com> Cc: Tim Kientzle <kientzle@freebsd.org>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org> Subject: Re: Wireless TCP aborts Message-ID: <4ab61a81003071756p1d5b273coa59cb6c075cb56fb@mail.gmail.com> In-Reply-To: <07C6C4E7-3512-4003-BDDE-DEDB549F6EA8@mac.com> References: <4B9425C4.5060309@freebsd.org> <07C6C4E7-3512-4003-BDDE-DEDB549F6EA8@mac.com>
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On Sun, Mar 7, 2010 at 1:08 PM, Chuck Swiger <cswiger@mac.com> wrote: > Hi, Tim-- > > On Mar 7, 2010, at 2:16 PM, Tim Kientzle wrote: > [ ... ] > > Corrupted MAC on input. > > Disconnecting: Packet corrupt > > rsync: connection unexpectedly closed ... [receiver] > > > > and then the rsync session is dead. > > > > It seems odd that a single corrupt packet would terminate the TCP > connection. > > It's not TCP itself which is closing the connection; if a garbage packet as > far as TCP or IP layer checksums was seen, it would be dropped and normal > resend mechanisms would compensate. However, SSH adds it's own layer of > data integrity checking called HMAC, which uses block-based hashes like MD5 > or SHA, and is much stronger than the 32-bit CRCs used at TCP/IP layers. > > See: > > /usr/src/crypto/openssh/packet.c > http://en.wikipedia.org/wiki/HMAC > > The implication is that the data is being corrupted before it gets munged > into network packets; failing memory is a likely cause, but bugs in the > network stack, the NIC driver, or OpenSSL are also lower-order > possibilities. > > Regards, > -- > -Chuck > > I have seen this same symptom many times with PCEngines ALIX boards but on the vr interfaces. It seems to come and go as I update kernels and worse yet, it seems to vary by board - have four boards all purchased at the same time a couple of years ago and some seem more prone to it than others. All have worked and failed at one time or another. I had, at one point, thought it to be related to power problems, because a high-power mini-PCI WiFi card seemed to exacerbate the problem, but removing the card made no difference, and the problem cleared up with an update and recompile of my source tree. It's a very disconcerting problem because FTP'ed files were being silently corrupted, so it's not just an SSH problem either. dave c
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