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Old 02-10-2011, 12:41 PM   #1
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PuTTY Fatal Error: Server unexpectedly closed network connection

Hi all, first off I would like to thank anyone ahead of time that may assist me with this. Also this is my first time posting a question here, and this question has to deal with PuTTy accessing HPUX, so not sure if this applies to this forum. I have seen other questions regarding this error in PuTTy which brought me to posting my question here... so enough with backstory and on to the issue!

I have a client that uses PuTTy to access their hpux system and he sporatically recieves the following error about 2 minutes after he enters his username/password waiting to get in;

PuTTY Fatal Error: Server unexpectedly closed network connection

Now I have looked all over the place but I can't come to a conclusion why this is happening. There is nothing in hosts.deny, which I didn't think would be the issue as he is able to login sometimes.

My client has 2 backend nodes he connects to, and it seems to only happen on one, and does not happen every time. Sometimes when he logs in he gets hung up and it seems like it will error out but ends up getting through.

I have tried turning on logging SSH packet info, but I honestly don't know how to interpret it or if I will get anything useful from them regarding the error.

Please assist

Last edited by pwwellons; 02-10-2011 at 12:52 PM.
Old 02-10-2011, 12:43 PM   #2
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No chance there is any specifically set administrative networks for the connection? Or possibly an intermediate firewall that notices the connection and drops the packets?
Old 02-10-2011, 02:10 PM   #3
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It sounds like less a putty issue than a network issue, but lets check some things.
Do both nodes have valid entries in the local DNS? In other words, do the names resolve properly? If not, try using "UdeDNS NO" in the sshd_conf file. The DNS checks can cause some delays that (in certain instances) can collide with timeout issues and cause odd behaviors.

Does the network latency match for traffic to each of the remote nodes? How do the ping results look? Check netconfig tables and see if any of the interfaces involved are stacking error counts. (You may have a duplex mismatch, or packet size collision: it happens.)


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