ssh: connect to host myhostname.ddns.net port 22: Connection refused

Question

I have recently set up a local machine and a laptop, using noip.com, so that I can access the local (host) machine, via my laptop whilst I'm away on a trip - see my previous question here

Everything worked fine - until I thought I would give the machine (and router) a cold reboot - before going away for a couple of months. After following all of the previous steps given to me in my previous questions, I find I can't login back to the server machine from my laptop.

Here are the salient facts:

1. Host machine (to be logged into) has SSH service running
2. Host machine has static IP address configured (same IP as I was using before)
3. No-IP update client is running on the host machine
4. I can SSH into host machine from my laptop, when I'm on the same LAN, by using the local IP address 192.168.x.x
5. The registered NO-IP address has not expired (I only registered it a few days ago - and I double checked by logging into my account - it has any correct public facing IP address)
6. Port forwarding has been set up on the router, with SSH running on the default port of 22.

[[UPDATE]]

$sudo ufw status
To     Action     From
22     Allow      Anywhere
22(v6) Allow      Anywhere (v6)

Fail2ban has been installed on the host machine and was working well with my previous setup. I have currently stopped the service, whilst I try to figure out what is going on.

SSH has been set up on the host machine with the following config:

• Port 22
• PermitRootLogin no
• PubkeyAuthentication yes
• PasswordAuthentication no

When I attempt to SSH remotely, using my registered hostname from no-ip, I get the following error (this used to work fine until yesterday):

ssh -v [email protected]
OpenSSH_6.9p1 Ubuntu-2ubuntu0.1, OpenSSL 1.0.2d 9 Jul 2015
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to myhostname.ddns.net [80.189.109.195] port 22.
debug1: connect to address xxx.yyy.zzz.123 port 22: Connection refused
ssh: connect to host myhostname.ddns.net port 22: Connection refused

Can anyone see what may be going wrong?. I have a flight in a few hours time, and I desperately need to get this sorted out, so I can remotely access my local machine from my laptop.

Answer 1

A few things to check, in order of most likely IME,

• Port forwarding. Unless your machine is directly accessible from the internet on 80.xxx.yyy.zzz, that's probably a router's address. You need to tell that router to forward traffic on Port 22 on to your computer. This is router-specific. The best single resource for this is PortForward.com.

  I see no mention of this here or on the previous question so this seems most likely.

• Firewalls can allow traffic from some locations and not others. I don't know what you've set up in this regard but if you're using UFW, sudo ufw status should let you see any deny/allow patterns that affect that port.

• /etc/ssh/sshd_config might be set up to only allow connections on a certain network. This isn't the default behaviour so again, this will have been something you've inadvertently done.

• If you've installed fail2ban, is it possible you've already triggered one of its its automated bans from your external IP?

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Before you push this onto the Internet using near-stock settings, I'd strongly suggest you read an article I wrote on making SSH secure. People get hacked through inadequate security practices all the time and a SSH server is a direct line to total control.