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Leo Simon
Asked: 2015-06-06 00:16:42 +0800 CST

ssh'ing from one computer to another on the same subnet

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I have two computers connected to the same subnet.

The first (A) is running 14.04, the second (B) 12.04

I can ssh from the first to the second, but not from the second to the first.

Don't really know where to start to figure out why there's this difference.

However nmap is giving quite different results:

Computer (A), which is the one I can't get into:

PORT    STATE SERVICE
631/tcp open  ipp

Computer (B), which I can get into:

PORT    STATE SERVICE
22/tcp  open  ssh
53/tcp  open  domain
139/tcp open  netbios-ssn
445/tcp open  microsoft-ds
631/tcp open  ipp

Since the only port that's open on both is 631, I've tried ssh'ing from B to A specifying port 631, but that doesn't work either.

Could anybody please advise how to proceed?

ssh

2 Answers

  1. Install openssh server on PC A. 

    sudo apt-get install openssh-server

    More details you have here

    Then you will can ssh into PC A from PC B

    SSH work on port 22.

    Edit 1

    If you have installed ssh-server on PC A you can check with command netstat -at do server expect connection on port 22

    This is output from my PC

    xxx@xxx:~$ netstat -at
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 *:microsoft-ds          *:*                     LISTEN
tcp        0      0 *:netbios-ssn           *:*                     LISTEN
tcp        0      0 *:ssh                   *:*                     LISTEN
tcp        0      0 *:ipp                   *:*                     LISTEN
tcp        0      0 *:telnet                *:*                     LISTEN
tcp        0    320 xxxx:ssh              xxx.xxx.xx.xxx:43423    ESTABLISHED
tcp6       0      0 [::]:microsoft-ds       [::]:*                  LISTEN
tcp6       0      0 [::]:netbios-ssn        [::]:*                  LISTEN
tcp6       0      0 [::]:http               [::]:*                  LISTEN
tcp6       0      0 [::]:ssh                [::]:*                  LISTEN
tcp6       0      0 [::]:ipp                [::]:*                  LISTEN
tcp6       1      0 ip6-localhost:38900     ip6-localhost:ipp       CLOSE_WAIT

    Important is:

    tcp        0      0 *:ssh                   *:*                     LISTEN

    If you set ufw or some firewall disable it and try connect then.

    Also restart ssh service

    sudo service ssh restart

    You will see if service start.

    • 1

  2. Thanks very much for your responses. I finally resolved this problem, thanks to the very helpful thread

    Bizarre SSH Problem - It won't even start

    The problem was that in the version of sshd_server that I downloaded with 

    apt-get install sshd_server

    There were three lines at the bottom of the sshd_config file that was installed, which proved to be the source the problem

    Host *
    ForwardAgent yes
    ForwardX11   yes

    When I removed these lines my remote login problems were resolved. To diagnose the problem, I followed the suggestion in the above thread, which suggested closing sshd with

    service sshd stop

    then running in debug mode

    /usr/sbin/sshd -p 22 -D -d -e

    In debug mode, sshd flagged the bad options in the default sshd_config file.

    After removing these lines, and restarting, port 22 was open.

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