Telnet Disconnects - Please help!

Harald Milz arv_bua_mharald at
Mon May 26 14:51:13 UTC 2008

Hi guys,

I've been working all day on getting this reproduced on a lab. I encountered one big problem. I am unable to recreate a 10-15ms delay from my ubuntu laptop to the Alcatel switch.

So it was a failure, because I created a +1500 line config on the Alcatel Switch and display it over and over again without getting disconnected.

I KNOW Alcatel switches aren't that popular, but CISCO ARE. And here is what I found out:

When connecting directly to a CISCO 6509 and executing "sh tech" (technical-information of the switch, including config blahblahblah...) the configuration was shown blasting fast, just like it should be. sh tech doesn't show the information with page breaks like sh config would (--MORE-- at the end of each page).

When connecting remotely to another switch that is 11.3ms away, and executing "sh tech", the technical-information was shown in "chunks". What I mean is, 50-80 lines are shown... 5 sec pause... 50-80 lines more... 5-10 sec pause... 50-80 lines more... 8 sec pause.... etc--but it does not disconnect!

I know lots of you guys administer CISCO switches and should be able to test this. REMEMBER it has to be +10ms away, if not, the issue does not reproduce.

The difference with Alcatel is that these above mentioned 'pauses' cause the connection to drop.

On the same laptop where I am running the tests, I have a windows partition, and I can view the configurations with no problems.

Any help on diagnosing this issue is appreciated!

KR, Harald

> Subject: RE: Telnet Disconnects - Please help!
> From: kauer at
> To: ubuntu-users at
> Date: Mon, 26 May 2008 22:39:38 +1000
> 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).
> Regards, K.
> -- 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Karl Auer (kauer at                   +61-2-64957160 (h)
>                  +61-428-957160 (mob)
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