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Old 02-03-2012, 09:06 PM   #1
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Registered: Feb 2012
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Question Cannot SSH via DNS from outside network

Hi everyone!

It's been a long while now since I've been out of the Linux world, and I'm very glad to be back

I have what I hope to be a rather simple problem. I have a box named running a fresh install of Slackware 64-bit V13.37 (no configurations of any sort have been made!)

I am able to SSH to the machine from another computer on the network via the machine's private IP addres and log in successfully.

When I try to SSH to the machine from via it's FQDN (ie., however, I get halfway there; I am able to reach the login screen and enter my username nad password, but I am unable to login. Running ssh with the -vvv option reveals that there is no response from the box (no rejection or anything); instead, it the connection is closed by the box after several seconds of waiting.

Anyone have any suggestions on how to fix this? I would greatly appreciate the assistance!

Other notes:
- I enabled port forwarding on my router: all TCP 22 packets go towards the box
- I am using the free Dynamic DNS service provided by; I already installed their client to automatically update my IP address and it appears to be working correctly since I can reach the ssh login of the machine; it's just not replying to my request to login.

Thanks again!
Old 02-03-2012, 09:28 PM   #2
Registered: Jun 2009
Location: Ambler, PA, United States
Distribution: Debian, Arch
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Hmm... Just for safe measure, does it work when you access the box using its WAN IP? I'm wondering if there's a config telling it not to accept connections from the Internet, and only work on your local net. Not sure though...
Old 02-03-2012, 09:48 PM   #3
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That is an excellent point! So here is the update:

IP assigned to router: (yes, I know this is a private address) - works

IP identified via - does NOTwork

Note: resolves to; specifically, I CAN connect but I receive no reply upon my attempt to login after submitting my password.

Last edited by Alexander11478; 02-03-2012 at 10:20 PM.
Old 02-04-2012, 01:09 AM   #4
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To be clear - this does not solve my problem since I want to access my machine via SSH externally. Anyone have any idea why I might be able to reach the login using either the external FQDN/IP address, but still not receive a response after I send my password packet?
Old 02-04-2012, 03:17 AM   #5
Registered: Mar 2007
Location: Spain
Distribution: Debian
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Check your ssh server logs, check your sshd_config file.
Since you have a longin, it doesn't seem to be a communication (fw, pf, routing...) problem. It seems to be a configuration problem to me.
Old 02-04-2012, 10:44 PM   #6
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I wish I knew what I was looking for. I've never set up sshd before, and I'm out of touch with all the layers of communication and authentication ssh has to go through before connecting. If someone could point me to specific options to play with, it would be most greatly appreciated. The options I have are all defaults for sshd. Again, I can connect from within the network, but do not get past the log-in screen when I try to connect using the public IP (I verified that my router wasn't blocking the service)


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