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SB-2 2014-08-08 Debian kernel 3.2.60-1+deb7u1
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Service bulletin: SB-2
Date: August 8, 2014

Between July 4 and July 20, 2014, the Linux kernel packages available
from Debian contained a bug that can significantly impact network
performance, especially bulk uploads. The broken kernel version is
3.2.60-1+deb7u1, and the fixed version is 3.2.60-1+deb7u2. The deb7u1
kernel fails to correctly handle packets with the Don't Fragment bit set
when generic receive offload is enabled on an interface. This results in
DF packets being dropped instead of forwarded. The most common symptom
is that download traffic works fine, while upload traffic stalls some or
all of the time.

Affected hosts
---------------

-  Aggregators and bonders imaged or upgraded between July 4 and July
   20, 2014
-  All architectures
-  Debian Wheezy only; Debian Squeeze nodes are not affected even if
   they were upgraded between July 4 and July 20

Solution
---------

To fix the issue, upgrade the kernel using the regular apt update
method, followed by a reboot:

::

    apt-get update
    apt-get upgrade
    reboot

If a site with the deb7u1 kernel is not experiencing issues, you might
consider delaying the kernel upgrade until the next time Bonded Internet
is upgraded on the node. You can see the installed kernel version of a
bonder or aggregator by visiting its Node Details page.

Workaround
-----------

You can work around the issue temporarily by disabling the “generic
receive offload” feature on a bonder, with this command:

::

    ethtool -K <interface of connected IP> gro off

For example, if the bonder has a connected IP on interface eth0, you
would run:

::

    ethtool -K eth0 gro off

This change is reset when the bonder reboots.

References
-----------

-  Debian bug report:
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=754173
-  Debian Wheezy kernel changelog: visit
   https://packages.debian.org/wheezy/linux-image-3.2.0-4-amd64, then
   click the link "Debian Changelog" (the link changes from time to time
   as the stable kernel version is updated)
