Window Scaling problems [was Re: Strange MTU-ish problem]

[D. Hugh Redelmeier]

| From: Timothy Murphy <gayleard at eircom.net>

| Maurizio Marini wrote:
| 
| > it's a known problem
| > http://forum.ubuntu-it.org/index.php?topic=235535.msg1625049
| > 
| > i have appended in sysctl.conf
| > net.ipv4.tcp_window_scaling = 0
| 
| Thanks very much.
| Molto grazie.
| That seems to have solved the problem for me.
| 
| It's strange that WiFi works fine with this router under Windows
| (XP and Vista), but requires this under Linux.
| 
| Since the only reports of the problem seem to have been from Italy
| I assume that the software setup on Alice (Telecom Italia) broadband
| is the cause of the problem.
| As far as I can see one has very little control over the router -
| eg I was unable to change the WPA-PSK key.

This problem is not just in Italy.  For example, the Toronto Public
Library site has this problem.

It is apparently caused by broken routers.  Potentially at your end or
the other end.  They are not conforming the RFC 1323 which was issued
in 1992!

These implementations are actively broken, not just ignorant.
They take an option (Window Scale Option) and change its value when
passing it through.  The RFC says that the presence of this option
does two things: it announces the value of the Window Scale factor and
it announces that the sender understands a Window Scale Option.  The
only sensible things for a router to do, even before this RFC were:
- drop the option, or
- pass it unchanged.
I cannot imagine any logic for passing it with a changed value.

See http://lwn.net/Articles/92727/

MS Windows Vista has problems with this too but has a work-around for
HTTP. See http://support.microsoft.com/kb/934430/en-us