Back to My Mac is an iCloud feature that becomes incredibly useful when you are working remotely from your office and need to get something done, or to help troubleshoot somebody else’s machine. According to, two-thirds of the U.S. Households that own Macs have more than one computer. Nearly three quarters of those households have laptops as well as desktops. A significant number of those Mac households also own iPhones, iPads, or other iOS devices. Free antivirus scan online. In the home, they might want to control a Mac mini-based home-entertainment server that has no monitor of its own. (If you all you really need is access to files on other computers, you might need only a file-synchronization service such as and; see for more.) Fortunately, there are plenty of ways to make such remote connections. They divide themselves roughly into five categories: • Tools built into OS X itself, including Screen Sharing and; • Chat services such as iChat and; • Dedicated online services including and; •; and • VNC. (For the purposes of these articles, we're looking at remote graphical control, and not Remote Login (using SSH). If you need that kind of access, chances are you already know all about it.) Unfortunately, it’s not always easy to figure out which one of those options will best meet your specific needs. And even if you’ve settled on a solution, it’s not always easy to get it to work. Why it’s hard Remotely controlling one Mac from another within the same local network isn’t especially difficult; Bonjour and other networking tools do a good job of that. Controlling a machine on a remote network is trickier; much of the networking hardware and software between the two is set up specifically to keep that from happening. Home networks typically use a combination of two technologies—Network Address Translation (NAT) and Dynamic Host Configuration Protocol (DHCP)—to provide Internet access to multiple computers through a single Internet address and to provide a light (not robust) buffer to keep strangers out of the network. They can keep you out, too. DHCP assigns private network addresses to the local computers. NAT then rewrites those addresses at the router, so that, to the rest of the Internet, all the traffic from those multiple computers seems to be coming to and from just one publicly accessible address. ![]() On business networks, firewalls and other filters further complicate any efforts to gain access. Some remote-access tools (particularly dedicated remote-access services such as Back to My Mac, GoToMyPC, and LogMeIn) take care of this problem by talking directly to a router’s NAT software and then mapping specific pathways into the network. Other solutions (including OS X’s built-in Screen Sharing software and VNC) require you to set up port mapping. (If IP addresses are like street numbers for apartment buildings, ports are like individual apartments at those addresses. A port is assigned to a particular service, such as file sharing or outgoing e-mail.) That means establishing persistent connections between ports on the router’s Internet-facing IP address and specific computers inside the network. If you’re lucky, NAT-PMP (NAT Port Mapping Protocol, favored by Apple) or UPnP (Universal Plug and Play, common on non-Apple hardware) on your router can take care of the port mapping for you. Third-party software such as ( ) or can also do the trick. (Another program, ( ), can create persistent connections between local networks, allowing for standard Bonjour hook-ups.) Port mapping manually is also doable, but it means learning the arcana of which ports are used for which services, how to assign persistent addresses or identities to computers on the network, and how to find your external public IP address (if your ISP you assigned one).
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