Remote Login - How is it done?

On the Mac, you just need to enable Remote Login (SSH, if you need it) and Personal Files under the Sharing menu. Make sure that these are allowed in the firewall.

Getting external access is the tricky part. You need to configure your router with either UPnP or NAT Port Mapping. For SSH, the port is 22, so you need to point your router to the IP of your iMac on port 22 (the iMac should have a static IP). There are two ports here, 22 for SSH, and the public port, which is what you use. For the public, use any port above 1023, as 1-1023 are reserved.

To get to your iMac, you should sign up with DynDNS.org. When done with DynDNS.org and the client install, make sure it is working.

Now, to access the iMac via SSH, type in dyndnshostname:publicport in Terminal as the SSH address.

Repeat this for each service (the DynDNS does NOT need to be reconfigured).

To have a fixed IP from the internet you can use No-IP.

No-IP is a nice service that you choose a name like "macwiz" and when you will end up with (for example) macwiz.no-ip.com, a point to your router at home, from there, just follow the macwiz1220 suggest.

You will need to install a small program that will upload your external IP into this service, so, even if you have a dynamic IP (like xDSL) you will have always your home router access using the DNS name that you choose.

Use SSH.

Ok this is basically what I also want to do but I am accessing a white macbook from a black macbook via the internet.

On the white macbook I want to access, I have allowed "personal file sharing" and "remote login" and the firewall has them open too.

The part I don't get is what you described here;

"For SSH, the port is 22, so you need to point your router to the IP of your iMac on port 22 (the iMac should have a static IP). There are two ports here, 22 for SSH, and the public port, which is what you use. For the public, use any port above 1023, as 1-1023 are reserved."

How do I do that for the white macbook. This white macbook accesses the internet through a Siemens Speedstream 6520 wireless ADSL gateway. How do I open these ports you described on this router?

Thanks for any help!

It sounds like you've not used the terminal much, if at all. As such, do not try using SSH for now. The "Remote Login" option requires you to log in with the "SSH" (Secure SHell), which gives you command-line access to your computer. It sounds like you want to do remote desktop "Screen Sharing", which is very much possible, but you'll need to either have a static IP address that you can manually enter into a remote computer's screen sharing client application, or some dynamic DNS service such as the "No-IP" one mentioned above, which keeps you from having to look up your IP address before you leave your computer.

Alternately there's the "Back to My Mac" service available by Apple, which does a pretty good job of providing a seamless persistent connection to your computer from any remote location.

I agree with Topher Kessler, if you dont usually work with Terminal or you have now UNIX experience dont use SSH.

Back to My Mac is a great option, go for that, works like a charm 🙂

Somebody else recommended "Chicken on the VNC". Which do you think is better? I haven't yet opened the ports on the router of the computer I am connecting to, but I already tried connecting through terminal and it eventually timed on, obviously because that port isn't open.

Once I open port 22, and if I tried the terminal thing again, what would be risky about a newbie using Terminal? I have used it a little before but I don't really understand it too much. I previously flashed the CD Rom on my old mac through terminal.

Once connected with SSH through terminal, would the other computer come up on finder?

OS X's built-in "Screen Sharing" application should work just fine, and if you decide to go with Apple's MobileMe solutions and use the "Back to My Mac" service, then it will be the most compatible option. However, if you do it manually then both "Screen Sharing" and another third-party client will work. The address to use would be "vnc://ip_address" where the ip_address is either your computer's ip (or the router's ip, as long as you have port forwarding enabled for port 5900 -- used for VNC), or the computer's name as long as you're on the local network.

An alternative to using port forwarding would be to use the SSH tunnel to establish a connection to your computer, but even this would require you to have port forwarding on your router for port 22 (SSH port). This is a more secure connection since SSH would provide encryption to the connection, but it's not necessary and might be more of a hassle to get things started.

To activate the "Screen Sharing" application, enter the VNC address into the finder's "Connect to Server..." option that's available in the "Go" menu. For Chicken of the VNC or other VNC clients, reference their documentation for how to connect.

I am having trouble after opening the ports. Still getting timed out using any of these options. I have another thread started about it here; http://discussions.apple.com/message.jspa?messageID=8459067#8459067
Any ideas as to why its not working?

If it's getting time outs, there's a good chance it's a firewall setting.