I'm pulling my hair out trying to get SSH to work through my router/firewall, tell me if I'm missing something...

Fresh install of Ubuntu Server 16.04, left SSH config alone, and created keys. Able to SSH to server inside of local network, all good there. Setup port forwarding on my router (22->22) (any->local ip address), cannot connect. Started a TCP port listener on another windows 10 machine and forwarded a random port to it, all good from the outside. Back to the Ubuntu machine, tried opening a TCP listener on a random port using netcat, forwarded that port to it, no go. I'm quite new to Ubuntu, I think must be missing something. UFW is off.

  • Suggest to use tcpdump, or wireshark if you prefer, to observe if the packets are arriving at your Ubuntu computer. sudo tcpdump -n -tttt -i interface_name port 22. If yes, then is sshd listening for any address? sudo netstat -tlnp. If you are trying from your work to home, note that often work doesn't allow port 22 out. – Doug Smythies Aug 21 '18 at 14:13

Well I found quite an interesting situation when I checked the ARP table of some other local machines. I had the server temporarily connected via WiFi through a WiFi extender that I keep in the garage. When an ARP request was sent out asking who had the IP address of my server, the WiFi extender was answering with it's own MAC address. The ARP table for any other host had the extender's MAC address associated with the IP address of the server. This doesn't usually seem to cause a problem even with multiple devices connected behind the extender, but apparently the NAT on my router was forwarding frames to the extender and it was simply discarding them for a reason that is not immediately clear.

What IS clear is that my understanding of range extenders is maybe not as great as I thought... also don't run servers off Wifi/Range Extenders even during setup.

Thanks for the tip Doug!

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