OS X Yosemite: If Back to My Mac doesn’t work
If you use Back to My Mac but don’t see your remote Mac listed in the Sharing section of a Finder sidebar, and your remote Mac connects to the Internet through an AirPort Base Station or AirPort Time Capsule, you may need to enable NAT-PMP (NAT Port Mapping Protocol) on the base station or AirPort Time Capsule. Your remote Mac uses NAT-PMP to automatically configure the base station or AirPort Time Capsule to allow computers on the Internet to discover it.
Open AirPort Utility, select your base station, then click Edit.
Click Network, then choose DHCP and NAT from the Router Mode pop-up menu.
Click Network Options, turn on Enable NAT Port Mapping Protocol, then click Save.
Click Update to restart the base station with the new setting.Note: The wireless network and all its services are unavailable until the base station restarts completely.
Back to My Mac can also use UPnP (Universal Plug and Play), which is similar to NAT-PMP, to configure some third-party routers. For information about enabling UPnP, see the router documentation or contact the manufacturer.