Back to my Mac’s Crazy Network Requirements

I gave Back to my Mac another try here at the airport. I discovered the following log entries in /var/log/system.log after enabling it in the .Mac preferences:

Oct 30 18:37:11 Leo mDNSResponder[16]:
  Adding registration domain thelameleopard.members.mac.com.
Oct 30 18:37:11 Leo mDNSResponder[16]:
  Setting up AutoTunnel address 1111:...:8888
Oct 30 18:37:14 Leo mDNSResponder[16]:
  Failed to obtain NAT port mapping from router 172.18.13.1
     external address 0.0.0.0 internal port 4500
Oct 30 18:37:37 Leo mDNSResponder[16]:
  Removing registration domain thelameleopard.mac.com.

What does this tell us? Well, it seems that Back to my Mac requires that BOTH SIDES are either on public IP or behind a router that supports UPnP or Apple’s own NAT-PMP. This so that BtmM can make a port mapping to allow incoming IPsec traffic on port 4500.

This makes no sense to me. There are barely any public hotspots that have UPnP or NAT-PMP functionality. The changes that Back to my Mac will work for road warriors is therefore dramatically reduced.

I really wish Apple had designed Back to my Mac with more real-world scenarios in mind. I understand their reasoning but with a little more effort Back to my Mac can work much better.