Why am I getting a connection timeout error with ssh?

Question

First of all, I'm pretty new to SSH. I've used it before, but never had to deal much with setting it up or navigating the details. Migrated from ServerFault.

Whenever I try to ssh to a public ip address from my windows 10 computer, I get an error that looks like ssh: connect to username@<public ip address> port 22: Connection timed out.

I can connect to my own linux machine from windows with a private ip address, and my windows machine connects to github with ssh public/private key authentication. My linux machine can connect to external servers (like AWS) via ssh, it's just my windows machine, and just public IP addresses, so far as I can tell.

Here's the output with the -vv option, and on a different port:

ssh -vv -p 2200 example.com                                                                                  OpenSSH_for_Windows_7.7p1, LibreSSL 2.6.5                                                                                       debug2: resolving "example.com" port 2200                                                                                       debug2: ssh_connect_direct: needpriv 0                                                                                          debug1: Connecting to example.com [93.184.216.34] port 2200.                                                                    debug1: connect to address 93.184.216.34 port 2200: Connection timed out                                                        ssh: connect to host example.com port 2200: Connection timed out   

What is causing this problem, and what do I need to do to fix it, so that I can ssh to external servers from my windows 10 computer?

I can ping external servers fine:

Pinging 1.1.1.1 with 32 bytes of data:
Reply from 1.1.1.1: bytes=32 time=23ms TTL=54 
Reply from 1.1.1.1: bytes=32 time=74ms TTL=54
Reply from 1.1.1.1: bytes=32 time=26ms TTL=54
Reply from 1.1.1.1: bytes=32 time=24ms TTL=54
      
Ping statistics for 1.1.1.1:
packets: Sent = 4, Received = 4, Lost = 0 (0% loss),                                                                Approximate round trip times in milli-seconds:                                                                              Minimum = 23ms, Maximum = 74ms, Average = 36ms

Answer 1

There are a number of reasons this could be happening - these are likely due to firewalling going on somewhere.

SSH sits on top of TCP. When you get connection timed out errors it means that the problem is that the SSH client is not seeing any responses from the server (ie the TCP handshake is not completing) which almost always means the problems is not with SSH, rather its at a lower level. This also explains why you get this error on ports that SSH is not listening on.

The first thing I do is examine firewall rules to check they are allowing SSH through. As the problem seems limited to your laptop/desktop, checking the local firewall and AV software is a good place to start.

If that does not solve it, break out traffic sniffers - seeing if the server receives and sends traffic is a useful hint. As its Linux, running something like

  tcpdump -n -i any src or dst XXX.XXX.XXX.XXX 

Can be useful where XXX.XXX.XXX.XXX is your external IP and where your monitoring us taking place from a computer not on the same man as your desktop.(maybe SSH to an intermediate server ie using a cellular connection or vpn?)

If its a complex network you may need to get your network administrator involved. If its a simple network where you are the network admin you might want to suspect an issue with port forwarding on your router and/or bad config related to this.

Using a VPN can "virtually move" the apparent point if your connection and can be useful for diagnosing/bypassing firewall issues.