network problems with kernel-2.6.17-1.2139_FC5

[George Avrunin]

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.

Thanks,

  George