RE: Telnet Disconnects - Please help!


----------------------------------------
From: mgb-ubuntu@xxxxxxxxxxxx
To: ubuntu-users@xxxxxxxxxxxxxxxx
Subject: Re: Telnet Disconnects - Please help!
Date: Mon, 26 May 2008 08:08:09 -0700

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!

Harald,

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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Mike, you've been very helpfull so far and I appreciate your willingness to assist on this issue so far.

But I have to disagree with your final comment.

I am more than willing to provide all the information required to get this issue resolved. Just need to get it reproduced on a lab. I am sure I am not the first person that cannot reveal company IPs, and should I be, I ask for the patience to be able to reproduce this in a way so that I can send you guys the correct information. Not all of us have the experience you have with Linux and if this List is only for Pro's then I'll stop sending mails, but I understand this list is also meant for ppl like me who have some knowledge just not the enough experience to be able to resolve issues like the one I am having.

You mention there is a way to reproduce network latency. But using a remote gateway as a route. I will try to find out if this is possible from outside our corporate LAN, within one of our DSL routers. I am even looking forward to setting up a DSL Router so that I can access it remotely without being on the corporate LAN. Just need some time.

The problem is curiously only affecting ubuntu. No Windows XP-Vista-2003, Debian, Red Hat or CentOS we have running, either in a VM or native, are experiencing this issue. All in the same network segment (within the same Class C).


KR,
Harald
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