Remote SSH connection

Networksshterminal

I want to connect my iMac remotely via ssh. Even though I can connect it locally, I can't do it remotely. When I try to connect remotely it refuses the connection.

port 22: Connection refused

I saw lots of discussions about the problem but w/o success. This is why I am opening a new thread.

I also disabled the firewall but still cannot connect. For diagnosing purposes, I executed netstat tupan and I see ssh local address as 192.168.1.33.ssh and Foreign address as 192.168.1.33.49883. Here is the output.

Proto Recv-Q Send-Q Local Address Foreign Address (state)

tcp4 0 0 192.168.1.33.ssh 192.168.1.33.49886 ESTABLISHED

tcp4 0 0 192.168.1.33.49886 192.168.1.33.ssh ESTABLISHED

tcp4 0 0 192.168.1.33.ssh 192.168.1.33.49884 ESTABLISHED

tcp4 0 0 192.168.1.33.49884 192.168.1.33.ssh ESTABLISHED

Could someone explain me what does this mean? Are those 49884 and 49886 are port numbers? Should I open new ports via port forwarding? And most importantly, could you guys explain me how can I connect remotely via ssh in layman terms please?

B.R.

Best Answer

Yes, the numbers 49884 and 49886 you see are indeed port numbers. However, they're not port numbers for the ssh service itself, but are the port numbers these specific clients have used for connecting. The numbers are essentially meaningless for you.

The usual problem that home users have with connecting remotely over SSH to their own computer is that their network is behind a NAT (Network Address Translation) router. Essentially this means that your router has a single public IP address, but allows multiple devices behind it to connect to the internet even though they have private IP addresses that are not "visible" on the internet.

The most common way to enable remote access over SSH is to add a port forward in the router. You'll need to port forward your remote IP port 22 to port 22 on the local IP of your iMac. How that is done depends on the exact router you have, but is usually explained in the manual or web interface help.

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It looks to me like you're using the wrong remote IP address in your tunnel. You should be using -L 5901:127.0.0.1:5900 ....

It's important to realize that the destination IP for the tunnel is where the remote (server) computer forwards the connection to, so 127.0.0.1:5900 means it connects to port 5900 on the server itself.

It looks like you're using ssh -L 5901:PublicIPofServer:5900 ..., which makes the server try to connect to port 5900 on its own public IP. But that's actually the WAN IP of the router the server's behind, so unless that router forwards port 5900 to the private IP of the server (in which case you wouldn't need the SSH tunnel) AND the router supports NAT loopback (aka hairpin NAT), this won't work.

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pharos and krb524 are both just guesses about network services, based on the service <-> port number listings in /etc/services; in this case I'm fairly sure they're both wrong guesses, so just think of them as identifiers for port numbers 4443 and 4444 respectively. To find out what's really going on, you need to find out what programs are connecting via those ports. You can do this with the lsof commands, like this:

sudo lsof -i:pharos -i:krb524

(you'll need to enter your admin password for sudo to get root access.) In the output, the important bits are the first two columns, which list the program ("command") names and process IDs of the processes that are using these ports. If the program name doesn't tell you what's going on, you can use ps and/or Activity Monitor to investigate those processes in more detail.

EDIT: If I'm reconstructing the lsof output correctly, it looks like this:

COMMAND   PID          USER  FD   TYPE             DEVICE SIZE/OFF NODE NAME
collabd    237 _teamsserver  7u   IPv6 0x7da9dd76981ec947      0t0  TCP localhost:pharos->localhost:50603 (ESTABLISHED
ruby       323 _teamsserver  31u  IPv6 0x7da9dd76981eeb47      0t0  TCP localhost:50602->localhost:krb524 (CLOSE_WAIT)
xcsbuildd 6943 _teamsserver  8u   IPv6 0x7da9dd76981ecd87      0t0  TCP localhost:50603->localhost:pharos (ESTABLISHED)

Those all look like components of OS X Server -- I'm not very familiar with the details, but collabd is a background process relating to "collaborative services" parts of OS X server, and the _teamserver user ID is used for those services. From comparing to my server, it looks like the ruby script handles notifications, and xcsbuildd is probably the Xcode build server. Apparently, they all talk to each other over ports 4443 and 4444.

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