Can I use Back To My Mac's mDNS address and for ssh and other routing of traffic?

On Lion and iCloud, the old MobileMe and Snow Leopard mDNS naming has changed and no longer works.

I'm wondering how to use command line tools to find out the DNS name that Apple has assigned to my Mac. I want to use that dns name on other devices that are not OSX (like Prompt on my iPad/iPhone) to ssh back to my Mac when I'm out and about.

Solution 1:

Update

There's a very simple way to simply SSH to a BTMM/iCloud computer:

In Terminal, in the Shell menu select New Remote Connection... (cmd+shift+K). From here you can browse by ssh/sftp/ftp/telnet hosts on the local or BTMM network.

This is obviously much easier for the individual apps that support iCloud/BTMM lookup (e.g. you'll also see file shares in the side-bar of Finder, and remote Airport devices in Airport Utility), but I'll leave the full instructions below for the more arbitrary use-cases.

For command line tools, Apple have replaced the old <computer-name>.<mobileme-name>.members.mac.com, with <computer-name>.<numeric-id>.members.btmm.icloud.com (where the <numeric_id> field is a number automatically generated for your Apple ID).

Step 1: Find out your iCloud BTMM domain

First, look up your domain using the DNS Service Discovery tool:

# dns-sd -E

The output is formatted slightly awkwardly, but what you're after is the numeric ID, which should be on the last line. You're after the full domain, something like 12345678.members.btmm.icloud.com, however dns-sd will display it (kind of) in reverse order, on separate lines:

23:41:33.309  Added                          icloud.com
                                             - > btmm
                                             - - > members
                                             - - - > 12345678

You'll also need to press ctrl+C after it displays the information you're after (it is designed to continue listening and updating). This applies to each use of dns-sd, here and below.

Step 2: List Computers

You can use these tools to browse that domain for services, e.g. for ssh servers:

# dns-sd -B _ssh 12345678.members.btmm.icloud.com

Or if you already know the hostname just access it directly as computer-name.12345678.members.btmm.icloud.com. (Any spaces in your computer name will be hyphens in this domain).

You can only access this from a computer that is also set up for BTMM on the same Apple ID account, because this hostname will resolve to an IPv6 address that is really the end of an encrypted network tunnel between your Apple ID's BTMM computers.

If you want to see the IPv6 address for a specific host, you can type

# dns-sd -G v6 computer-name.12345678.members.btmm.icloud.com

And it'll display something like:

17:37:47.504  Add     2  0 computer-name.12345678.members.btmm.icloud.com. FD11:993E:64AE:4DEA:011F:FBD1:F444:11A1%<0>  152

Step 3: Connect

# ssh [email protected]

Note

I'm not sure if that number will ever change, so you may or may not need to repeat Step 1 at some point later on... mine's been static for quite a few years now.

Solution 2:

This isn't my preferred method, but the Terminal app also polls your iCloud account for all Back To My Mac computers that it has a current registration.

Under the Shell menu - New Remote Connection... ⇧+⌘+K

This is quite handy to set up a new ssh/sftp connection home when you are not on the local internet or your dns server won't look up the AAAA records that match your current host.12346789.members.btmm.icloud.com. domain reservation.

Solution 3:

Here's the answer to your question…

I just learned a nifty way to find your BTMM domain name

echo show Setup:/Network/BackToMyMac | scutil | sed -n 's/.* : *\(.*\).$/\1/p'

source: https://gist.github.com/1856804 by skyisle

But here's why that still doesn't help you…

However, note that even if you know the BackToMyMac domain, you can only use it if you are connecting from a computer that is connected also logged into 'BackToMyMac'. It will not work directly via Prompt.

(I believe Apple considers this a security-related feature. Otherwise anyone on the Internet could try to gain access to your Macs if they knew the BTMM domain name.)

There are other sites on the web which will do dynamic DNS hosting for you. I've used DynDNS for years, but they have gotten more and more commercially focused (used to be able to get 5 free dynamic hostnames, now it's 1, and you can only get that one by giving them a credit card number and trying out one of their premium services and then canceling it).

I have not used http://www.no-ip.com/ but they have a Mac update client too (which will automatically update whenever your Mac's IP address changes) and they will give you three free hostnames if you create a free account (no credit card info needed).

Note that this doesn't work as easily as BTMM because you still have to make sure that you have open ports on your router, etc. However, it will work with Prompt and from other hosts.