Date: Sun, 11 Nov 2007 23:23:23 +0100 From: Andre Oppermann <andre@freebsd.org> To: Gregory Wright <gwright@antiope.com> Cc: freebsd-current@freebsd.org Subject: Re: excessive TCP dulplicate acks revisted Message-ID: <473780DB.2040705@freebsd.org> In-Reply-To: <C621C4E4-4230-4658-B668-A0612B632565@antiope.com> References: <46B41421-3112-40C6-84D9-094FA771F93E@antiope.com> <4735CE3A.7020905@freebsd.org> <C621C4E4-4230-4658-B668-A0612B632565@antiope.com>
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Gregory Wright wrote: > > On Nov 10, 2007, at 10:28 AM, Andre Oppermann wrote: > >> Gregory Wright wrote: >>> (Note: long message) >>> Hi, >>> The tcp duplicate ACK attack is back. >>> Last March, there was a thread on duplicate TCP acks in -CURRENT. >>> I have been able to reproduce the problem on 7.0-BETA2 (amd64) >>> and have some new information that might help locate the bug. >>> Background: I first noticed problems with tcp connections dropping >>> when Bacula was running on our backup server. The hardware was >>> a dual Opteron 244, 2 GB RAM, running FreeBSD 6.2-RELEASE-p2. >>> The ethernet NIC was a bge. >>> We went through an extensive process to rule out hardware and cabling >>> problems: the server hardware was replaced with a single Opteron 270 >>> (dual core) on a Tyan S2882-D motherboard. The memory was replaced >>> as well. The NICs are still bge. This machine is "hardtack". >> >> This may be a TSO bug in the bge hardware. Please repeat your tests in >> the original setup with TSO disabled on the bge interfaces ("ifconfig >> bgeX -tso"). >> Second if you've got another network card with something else than bge >> please put it into the same box and run the tests as well. >> >> --Andre >> > > Hi Andre, > > I also took a look at the bge (4) driver in 7.0-BETA2. As far as I can > tell, > it does not support TSO (there is no ioctl supporting TSO enable/disable > as there is for the em(4) driver). OK. > Might the chip --- a BCM5704_B0 --- not be completely initialized? This > might explain why the machine with the BCM5714_B3 chips works, while > the other machine shows the duplicate ACK bug. Perhaps. Do you see the duplicate ACKs in a tcpdump on both the sender and the receiver? If you see it on the sender too, then it must be a bug in our network stack or the driver (by requeuing the same packet over and over again). -- Andre
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