Connecting to Computers Beyond Your Local Network
One limitation of relying on Bonjour for connection is that only computers on the same network or network segment can be located.
You can, however, connect to computers on other network segments if you know their IP addresses. If your remote Mac is connected to the Internet directly or if it is connected by a router that has port forwarding configured for port 5900 (the standard VNC port), you can connect to it from anywhere on the Internet.
To do this you’ll need to launch the Screen Sharing application manually. The application is located inside the Core Services folder along with several other Mac OS X components that are normally launched as part of operating system (including the Finder).
This folder is located at the following path (beginning at the root level of your hard drive): /System/Library/Core Services. You can make an alias of the Screen Sharing application to store in a more convenient location or add it to the Dock for easy access.
When you launch the Screen Sharing application manually, it will immediately ask you for the IP address or host name of the computer to connect to.
If you are connecting across the Internet, you’ll need to know the public IP address for your computer (i.e., the one provided by your ISP), not the internal IP address provided by your router.
As mentioned above, you’ll need to configure port forwarding for your router (refer to the documentation of the router for instructions). If your ISP uses DHCP to assign IP addresses (most do), the IP address may change periodically.
One solution to this is to sign up for DynDNS, a service that allows you to assign a DNS name (such as mymac.dyndns.org) to your Mac or router (many, though not all, routers support dynamic DNS updating).
When the IP address provided by your ISP changes, your router or software on your Mac can notify the DynDNS of the new address, which in turn updates the DNS name to point to the new address.
If you want remote access to your Mac via the Internet, but without the hassle of configuring a router for port forwarding and setting up a DynDNS, you can sign up for a .Mac account.
.Mac offers a number of features, including the new Back to My Mac feature, which essentially allows Leopard to automatically do all the updating of your IP address and connecting through your router for you. All you need to do is enter your .Mac information on both computers and enable Back to My Mac in the .Mac pane in System Preferences.
Whenever you’re connected to the Internet, you’ll see your other Back to My Mac–enabled computers in the Shared section of the Finder’s sidebar as if they were both on the same network. You can connect for file sharing or screen sharing as you would if you were on the same network.
This feature truly offers a lot of value to .Mac in Leopard because it gives you consistent remote access to your Macs and files, regardless of where you are, with almost no effort in configuration.
One concern with using screen sharing with Back to My Mac is that access to your remote Mac is managed using your .Mac account information. To help secure your Mac in the event that your .Mac account is ever compromised, you should use a screen saver and require a password to wake the computer, as mentioned earlier.