network problems with kernel-2.6.17-1.2139_FC5

[Roy Erickson]

On Jun 27, 2006, at 2:20 PM, George Avrunin wrote:

>
> I've just updated to the 2139 kernel and I'm encountering some network
> problems.  Connections inside my department seem fine but connections
> to anywhere outside (other departments on campus, the rest of the
> world) lock up after some fairly small amount of traffic.  The
> problems disappear if I reboot back into the 2133 kernel.
>
> The symptoms are very similar to some that I recall from a couple of
> years ago with the move to the 2.6.7 kernel where some of the
> networking parameters changed.  At that time, there were problems with
> various firewalls/routers and the solution was to do
>    sysctl -w net.ipv4.tcp_default_win_scale=0
>    sysctl -w net.ipv4.tcp_moderate_rcvbuf=0
> (or the equivalent in /etc/sysctl.conf).
>
> tcp_default_win_scale doesn't seem to exist anymore, but setting
> tcp_window_scaling to 0 seems to work, at least as far as I've been
> able to check quickly.  But I don't really understand what these
> parameters represent and don't want to mess things up.
>
> Can the gurus tell me what, in words of one syllable, what changed in
> this respect from the 2133 kernel to the 2139 and what the right fix
> is?  What am I losing if I set tcp_window_scaling to 0?  I have some
> influence on the settings of my department's network equipment, but
> the connection to the campus backbone is controlled by the Office of
> Information Technology, which generally doesn't respond well to
> requests from Linux users in the science and math departments.  So if
> it's a question of me changing things on my Fedora boxes or OIT
> changing settings on its network equipment, I'll be the one making the
> changes.
>
Try http://kerneltrap.org/node/6723

From: John Heffner [email blocked]
Subject: Re: 2.6.17: networking bug??
Date: Tue, 13 Jun 2006 13:39:42 -0400

Mark Lord wrote:
 > John / David: Any ideas on what's gone awry here?
 >
 >

Yes, you have some sort of a broken middlebox in your path (firewall,
transparent proxy, or similar) that doesn't correctly handle window
scaling. Check out this thread:
<http://marc.theaimsgroup.com/?l=linux-netdev&m=114478312100641&w=2>.

The best thing you can do is try to find this broken box and inform its
owner that it needs to be fixed. (If you can find out what it is, I'd
be interested to know.) In the meantime, disabling window scaling will
work around the problem for you.

-John

From: Linus Torvalds [email blocked]
Subject: Re: 2.6.17: networking bug??
Date: Tue, 13 Jun 2006 10:50:51 -0700 (PDT)

On Tue, 13 Jun 2006, John Heffner wrote:
 >
 > The best thing you can do is try to find this broken box and  
inform its owner
 > that it needs to be fixed. (If you can find out what it is, I'd be  
interested
 > to know.) In the meantime, disabling window scaling will work  
around the
 > problem for you.

Well, arguably, we shouldn't necessarily have defaults that use window
scaling, or we should have ways to recognize automatically when it
doesn't work (which may not be possible).

It's not like there aren't broken boxes out there, and it might be  
better
to make the default buffer sizes just be low enough that window scaling
simply isn't an issue.

I suspect that the people who really want/need window scaling know about
it, and could be assumed to know enough to raise their limits, no?

Linus

> Thanks,
>
>   George

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