excessive TCP dulplicate acks revisted

Gregory Wright gwright at antiope.com
Sat Nov 10 20:11:15 PST 2007

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).

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.


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