Sign up ×
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It's 100% free.

Running Ubuntu 12.04, I've set up the OpenSSH server. I can connect from within LAN, but not from outside. I am using the same sshd_config file as on my other Ubuntu 12.04 machines (that sit in a different LAN).

$ ssh

works fine, but

$ ssh

(made up IP address) does not work. Nothing happens. No error message, or anything. The prompt just sits there.

Thanks to comments below, I have managed to verify via websites and ShieldsUP that port 22 is indeed open.

Using the option -vvv, I get the following:

$ ssh -vvv
OpenSSH_5.9p1 Debian-5ubuntu1.4, OpenSSL 1.0.1 14 Mar 2012
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to [] port 22.
debug1: Connection established.
debug1: identity file /home/myname/.ssh/id_rsa type -1
debug1: identity file /home/myname/.ssh/id_rsa-cert type -1
debug1: identity file /home/myname/.ssh/id_dsa type -1
debug1: identity file /home/myname/.ssh/id_dsa-cert type -1
debug1: identity file /home/myname/.ssh/id_ecdsa type -1
debug1: identity file /home/myname/.ssh/id_ecdsa-cert type -1

And then the prompt just sits there.

Further debug information from var/log/auth.log:

$ grep sshd /var/log/auth.log
[cutting old lines...]    
Jul  6 10:23:05 mymachine sshd[7871]: Did not receive identification string from

I am allowing any user to connect, in particular my own username. What confuses me is that I have not had this problem on any other machine, although they are on a different lan. This lan has only one computer attached to it. Any ideas of how to proceed from here?

share|improve this question
try using the verbose option (-v, -vv, to -vvv) to get extra info re: the connection. e.g., ssh -vvv -p 51555 – amc Jul 5 '14 at 20:57
check the forwarding port – hwez Jul 5 '14 at 21:00
Thanks, I have edited my question to reflect your comments. – DustByte Jul 6 '14 at 8:05

4 Answers 4

Need to check that port forwarding is working correctly i usually check by going to > Proceed > put your port number in the box and click user specified custom port probe. That should tell you if that TCP port is in fact open to public

share|improve this answer
Thanks. I've edited my question to reflect your suggestion. Problem remains however. – DustByte Jul 6 '14 at 8:06
HUH well the network is ruled out so looks like a config issue. Try grep sshd /var/log/auth.log – meccooll Jul 6 '14 at 8:17
The following line is then added to auth.log: Jul 6 10:23:05 mymachine sshd[7871]: Did not receive identification string from – DustByte Jul 6 '14 at 8:29

Are you declaring a user?

ssh Jimmy@ -p51555

If you gave the code the way you are using it then I believe that it will default to the current user name.

Furthermore, you need to have a user on the TARGET system with permission. in the above example "Jimmy"

share|improve this answer
I have indeed. I am only connecting with the same user all the time, and further, sshd_config allows any user to connect. – DustByte Jul 6 '14 at 8:07

A couple of things for you to check.

  1. Check /etc/ssh/sshd_config and make sure that you don't have any funny AllowUsers entries.

  2. Specify the user that you want to connect as:

    ssh SERVER -lUSER
  3. Check your firewall (iptables):

    sudo iptables -L --line-numbers
    sudo iptables -L -t nat --line-numbers
share|improve this answer

Check your gateway on the SSH server is set to the router doing the port-forwarding.

route -n

The default route should point back to that router, otherwise, you will be able to initiate connections through it, but the ACK's won't go anywhere!

share|improve this answer

protected by Community Aug 8 '14 at 8:08

Thank you for your interest in this question. Because it has attracted low-quality answers, posting an answer now requires 10 reputation on this site.

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.