Cfrgtkky

I set up a remote Ubuntu machine a few weeks ago and I was able to ssh into it without any problem. This until a few hours ago, when the machine stopped responding, and I tried to start a new session.
Now I just get:

ssh: connect to host IP port XYZ: Operation timed out.

Unfortunately I am not able to have physical access to the machine so I'm trying to figure out what the problem could be. I tried:

ping IP

but I keep getting Request timeout for icmp_seq 0. My family tried to re-boot both the machine and the router, but it didn't help. Any suggestion?

P.S.: I'm new to setting up remote machines, so I'm sorry if a didn't include relevant information to answer my question.

Apparently one problem was the IP of the router that changed during my ssh connection. I still have problems but are probably related to the machine, and not to the network.

There could be many reasons it stopped working. Without physical access it is impossible to know.

However, based on your question this is a machine you set up at your families home. The first thing that comes to mind is the router's IP address changed. This is common for residential router's that use DHCP leases. Or perhaps the router got reset and the port forwarding for SSH is gone. It could be the SSH server isn't starting. The list goes on and on.

Ultimately, relying on ssh to keep working on a network that you don't manage directly is a tough proposition.

In order of likelihood:

The router IP is assigned dynamically (through DHCP, for example), and its lease expired, so the router acquired another IP and the one you have has been reassigned to another ISP customer.

Diagnostic: ask someone onsite to visit whatismyip.com or a similar service and read the IP to you. If you managed to successfully ping the IP in the past, your failure to ping now might indicate the old ip was unassigned and not reassigned, but it's not conclusive.

Fix: connect to the new IP. The long-term fix is to use a dynamic DNS service in the future (noip is popular, for example)

The router is down / malfunctioning, or the connection to the ISP is broken

Diagnostic: ask someone onsite to browse the internet. This would also cause ping failure.

Fix: either help troubleshoot, or dial the ISP

The router firmware was upgraded or reset, and your port forwarding settings are gone.

Diagnostic: if possible, ask someone onsite to visit the browser page and double-check the settings. Ping should still work.

Fix: Re-add settings. To prevent it from happening again, you can setup a automatic SSH reverse connection (-R). You can combine that with autossh for robustness, or even setup a VPN client such as openvpn, if you're feeling ambitious.

The ISP decided to firewall port 22. This is unusual, but not unheard of.

Diagnostic: setup SSH on a new port, both on the computer and the port forwarding on the router. Ping should still work.

Fix: Just use another port or dial the ISP

As the question why SSH might no longer work has already been answered (public IP changed, port forwarding rule reset etc.)
I wanted to respond to the fact the ping timed out:


Ping doesn't use any ports because it doesn't use TCP / UDP but rather ICMP. This means if you pinged the public IP you pinged the router connecting the server to the internet, which most likely didn't answer ping for security purposes (most residential routers do this).


If you pinged the private IP address of the machine (192.168.x.x or something like that) the router you use to connect to the internet won't forward the ping because 192.168.x.x is a private IP address range, meaning requests to such IPs wont be forwarded through the internet.