Ben Kevan’s Blog

Kernel tcp_output “work around” implemented for openSUSE 11.1 Beta 5

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As some of you may have followed there is a bug in the 2.6.27 Kernel branch that was introduced when the order tcp output was changed when cleaning up some code. Here is the original commit that introduced the bug.

Ilpo jarvinen clears up some rumors about the bug:

There are some analysis which are claimed to be “very good” circulating around
which tell you that Linux now enabled timestamps in 2.6.27. Sadly that is a
_false_ claim, the timestamps were _not_ enabled for 2.6.27 (or -rc1). Don’t be
fooled wide-spreadness of the claims, sadly multiple distros seem to repeat and
support the false claim in their “semi-official” documentation. Timestamps have
been enabled already for a very long time before 2.6.27…
The real change that happened from 2.6.26 to 2.6.27, as described in the commit
which fixes this particular bug, was a change in the _order_ of the TCP options
(timestamps are tcp options). The order change was not intentional, not that it
should have broken something. The correct fix is to restore the original
ordering. …It is very easy to verify with tcpdump if 2.6.26 does send
timestamps or not (hint: look into SYN packet’s TCP options).

In the original bug report.

Want to know more about this issue, check this page out

Note: I realized that I called the issue a “bug” however it really isn’t a bug in the 2.6.27 kernel, but the non compliance of other hardware in the way it handles the tcp_output, since they shouldn’t care about the order (which is the standard).

Sorry I couldn’t write up more about it.. a bit busy today at work.

Tags: kernel, opensuse

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