Telnet Disconnects - Please help!

Smoot Carl-Mitchell smoot at
Mon May 26 17:43:32 UTC 2008

On Mon, 2008-05-26 at 22:39 +1000, Karl Auer wrote:
> On Mon, 2008-05-26 at 05:26 -0700, Smoot Carl-Mitchell wrote:
> > echo 0 >/proc/sys/net/ipv4/tcp_window_scaling
> > 
> > If window scaling is not negotiated properly, then you will experience
> > "freezing" on receiving large amounts of output from the router or
> > switch.
> But it doesn't freeze. The connection is terminated abruptly. Or did I
> misunderstand the OP's description? (which I no longer have).

My only point is you can turn window scaling off on the GNU/Linux box
and see if the problem goes away.  If it does, then that is the source
of the problem.  If not, it at least eliminates it as an issue.

I experienced the "freezing" issue with a hotel ISP which evidently had
switches or routers which did not negotiate window scaling correctly or
at all.  It took me several hours to figure out what was going on.  I
tracked down the problem by using tcpdump and watching the packets go
by.  My TCP keep sending timeout ACKS, while the remote TCP refused to
send anything. I suspect the remote end thought my TCP's receive window
was zero, even though my TCP kept telling it the receive window was wide
open. The window scaling interfered with the TCP negotiation in some
peculiar way.  I suspect it was an old implementation which did not
support window scaling at all and ignored the initial negotiation.
Smoot Carl-Mitchell
System/Network Architect
smoot at
+1 480 922 7313
cell: +1 602 421 9005

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