Establishing ssh session using Back To My Mac
"Back to my Mac" uses a special tunnel device configured with two - more or less random and unique - IPv6 addresses from the local address room:


a link local address: fe80...
a unique local unicast (ULA): fc00… to fdff…


All IPv6 traffic (computer_name.number.members.btmm.icloud.com is the DNS name of a IPv6 host/device!) is wrapped into IPv4 packets, so that a IPv6 capable router isn't needed. On the Apple side it's unwrapped - probably with some 6in4 relay - and then routed to the remote device.

Apparently this doesn't work if you want to ssh from your own host into your own host (aka ssh -6 %localhost-utun1-ULA%). It works with a second device (also registered with your Apple ID in iCloud) in your own private or a remote network.

It's really slow though (tested with two Sierra VMs on one hosting Mac all using the same physical network interface!).