Slingbox working with Airport Express but now Back To My Mac broken

Question

I had Back To My Mac working a couple of months ago. I have a Mac Mini connected to a Time Capsule on my Roadrunner cable modem network, and I had a Slingbox Pro (SBP) connected to my DSL Airport Extreme(n) network. I carry a MacBook Air with me on trips.
I wanted to move the DSL Airport Extreme to another room and needed an ethernet connection for the Slingbox, so I bought the Airport Express, plugged it in, and configured it to extend the Roadrunner network. I plugged the SBP into the Airport Express and configured the AE for port forwarding. So my two networks look like this:
Roadrunner ---> Time Capsule ---> Mini (via ethernet), and
Roadrunner ---> Time Capsule ---> Airport Express(n) (wirelessly) ---> SBP (ethernet)
DSL ----> Airport Extreme ----> wireless network 2
Now when the MBA is configured on the Roadrunner wireless network I can see and access the Mini. When I change networks, either using my own DSL network or out of town on a hotel network, the computers cannot see each other and BTMM will not work. Does anyone have any ideas on how I can configure either computer or the network components to get this working again? Thanks. I will also post this in the .Mac forum.

Answer 1

The Slingbox Pro connection works because Slingbox has its own system for keeping track of the WAN IP address of the Time Capsule.
Unless your Time Capsule has an assigned static WAN IP address, you need to set up your own system to do this for the purpose of file sharing from the MBA to the Mac mini from the DSL network or from the Internet. You can use a DNS hosting service such as DynDNS for this purpose. See: http://www.dyndns.com/
You can set up a free account with DynDNS and install client software on your Mac mini that notifies the DynDNS server whenever the WAN IP address on your Time Capsule changes. You assign a static LAN IP address to the Mac mini and forward UDP and TCP port 548 from the Time Capsule to the LAN IP address of the Mac mini.
When you want to file share to the Mac mini, you can use the Connect to Server... function in the Finder using this address (as an example):
afp://xxx.dyndns.info
The DynDNS server converts the "xxx.dyndns.info" placeholder to the current WAN IP address of your Time Capsule, and you end up connecting to the Mac mini—either from the other network or from the Internet.
You also may be able to use the Back to My Mac function with a .Mac account, but I am unfamiliar with it and have never tried to use it.