Telnet Disconnects - Please help!

Mike Bird mgb-ubuntu at
Mon May 26 15:08:09 UTC 2008

On Mon May 26 2008 07:51:13 Harald Milz wrote:
> 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!


Many of us have administered switches that are tens if not
hundreds of milliseconds away.  You can force a long delay
simply by bouncing a route through some tunnels off a remote
router or server.  I ran some scenarios using netcat with a
slow sink and could not reproduce your problem.

It's 99.9% certain that the problem lies outside Linux - either
inappropriate filtering or maybe the Alcatel can't handle window
scaling as Smoot suggested.  Who knows?  Unless you provide
sufficient information you're just wasting list bandwidth.

If you need confidential assessment of a pcap, there a hundreds
if not thousands of us network consultants out there that your
firm can hire by the hour or by the day.

--Mike Bird

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