I hope someone can help me troubleshoot this ssh login issue. In my home LAN, I develop websites and have set up my router to forward external SSH calls to my main laptop from this external port.
So if I'm logged into a customer's computer I would ssh, or scp
$ ssh -p 7219 sam@mycomcastip
which worked well until a few weeks ago when I upgraded it to Mojave. Now the connection times out. Here's my steps to isolate the issue:
$ ssh -p 7220 sam@mycomcastip
works because my router port forwards it as port 22 to an older machine running High Sierra. Maybe my router is goofed? I thought so, so I installed OpenWRT on it (which is very good, so far) and I cannot ssh into the laptop from outside as I could before.
Perhaps Comcast is blocking port 7219? It if was, it would be blocking port 7220 and it's not blocking it. Changing the port forward to another port fails with the same timeout.
Perhaps it's my SSH daemon that's goofed? Changing the port forward to route to the laptop's port 80 (which has Apache running), instead of 22 yields no difference in the result.
I can confirm that inside my LAN I can SSH into this laptop with no issues. That assures me that the laptop's ssh daemon is running. I have no trouble ssh out from this machine.
I can confirm the router is not doing the blocking because I can run tcpdump on the router looking for this port and it receives it and passes it on.
tcpdump on this laptop and examining the PCAP in Wireshark I can see the packet coming in on port 22 and subsequent attempts by the remote operator retrying the connection, but I just haven't found the right tutorial on analyzing a packet for this issue to help me see what might be the cause.
41 3.349934 remoteIP 192.168.1.105 TCP 74 45166 → 22 [SYN] Seq=0 Win=14600 Len=0 MSS=1460 SACK_PERM=1 TSval=1415111467 TSecr=0 WS=512
Perhaps someone can shed light on what this means?
I attempted to install Mojave on another machine to see if it is a Mojave issue but every other machine is too old to run it so I'm unable to isolate that it's the hardware or software on this machine. Speaking of which, this behavior occurs when I'm routing to the laptop through the wireless and Ethernet/Thunderbolt of the laptop which would suggest that if it's hardware, it's not the networking ports causing the issue.
Since the port forwarding rules are the same except for the source and destination ports, I'm leaning on thinking something changed in Mojave as that's the only change I've recall that I made to the laptop when this capability broke.
Looking online, I found the closest which suggests that Apple has closed off certain folders to remote users. Except as this poster determines, SSH gets around this block so that may not be it.
I discovered a clone of this machine on High Sierra before I upgraded it to Mojave. Running off that clone, the expected behavior occurs. Running tcpdump on this laptop I can see the TCP passed through the router to this laptop from the remote server and I can see my laptop is ACK in return, which confirms what I saw when I SSH in from remote. That seems to eliminate that it's my firewall on the router that is blocking any of these odd ports to this laptop. Which points more likely that Mojave is blocking port 22 from outside its subnet.
I can show screen cap that shows this Mojave firewall is turned off if important.
That's why I ask here, instead of another networking forum as it seems to be only the Mojave OSX machine that is rejecting port 22. What other troubleshooting steps should I try?