Marco.org

If you have MobileMe, you can access your Back To My Mac-enabled computers via SFTP and SSH (if enabled in Sharing) with this hostname:

computer.username.members.mac.com

…where computer is the hostname and username is your MobileMe username (before the “@”).

But if your hostname or username contains a dot or other special character that isn’t normally permitted in DNS, it becomes tricky. You can see how the hostname is encoded by opening Terminal and selecting File→New Remote Connection…, then Secure File Transfer (sftp), then the target hostname under Server, and see how it encodes it on the command line in the bottom text field.¹

If your MobileMe username was john.doe@me.com and your computer was called John's iMac, it would show this:

sftp -oPort=22 Johns-iMac.john\.doe.members.mac.com.

The backslash isn’t a valid DNS character. Leaving it in, double-escaping it, omitting it, or replacing with a literal period all don’t work for most common commands like ssh, ping, or dig.

Because it’s actually an IPv6 address.

Disclaimer: I know absolutely nothing about IPv6.

So it actually does work with IPv6-enabled commands:

ssh -6 'Johns-iMac.john\.doe.members.mac.com'
ping6 'Johns-iMac.john\.doe.members.mac.com'

If you enable Remote Login (SSH) and set up the SSH connection with password-less keys, you can get your computer’s external IP and avoid the need for DDNS for certain uses (like many of mine).

HOME_IP=`ssh -6 'Johns-iMac.john\.doe.members.mac.com' \
    curl -s 'http://whatismyip.org/'`

I’ll be shocked if more than zero people who see this can actually use this information, but it has been eluding me for months and I finally figured it out.