For those that are unfamiliar with the relatively new tunnel feature that is supported in versions 3.0.1, 3.0.2 of BBHN, and version 3.1.0 of the AREDN firmware, perhaps this information will be helpful.
The basic idea is to provide an alternate path via the Internet as a substitute for a RF path. Hopefully this will be used as a temporary solution. A basic concept of an independent, free standing mesh network is to provide connectivity when the Internet fails. So why would you want to connect with the Internet in the first place?
One reason is to connect "mesh islands"; two or more established mesh networks that are isolated from each other by a long or difficult RF path. Perhaps this path will be achievable in the future with some intermediate nodes. In the meantime, an Internet tunnel can be used to connect the networks. A mesh network in the far West Valley wanting to connect to an East Valley network would be an example.
Another application would to demo or monitor a mesh system from a remote location.
As implemented in the newest firmware, the underlying "hooks" for the required tunnel software are there, but the software is not actually installed. There are two separate packages, a tunnel server and tunnel client.
A complete tunnel consists of a server and at least one client. One server can handle multiple clients. The nice thing about the way this is done is that the "stock" mesh firmware functionality including the webGUI and radio are identical to the unmodified firmware. That means if you are connected to the mesh by way of a tunnel client you will see the exact same view of the network and have the same access to the resources on the mesh as a node connected by radio. It also means the radio in the tunnel client can pass on mesh connectivity to other nodes.
The tunnel software can be installed on both Ubiquiti and WRT54 platforms. Each has advantages for a particular situation. If the main goal is simple connectivity to the mesh and the radio is not much of a concern, a WRT54GS (version 1-3) with 32MB ram and 8MB flash is ideal. Both the tunnel client and server need both WAN and LAN connections and the WRT32GS has a built-in LAN switch and a separate WAN port. The biggest problem is finding a GS v1 to 3. The newer versions 4 on up of the GS won't work; the amount of ram was reduced back to 16MB and the tunnel software needs more memory.
If the tunnel client node can be mounted outdoors and connected to an effective antenna, then one of the Ubiquiti radios would be the way to go. All the BBHN supported Ubiquiti products have enough memory to install the tunnel software. The only issue is that the Ubiquiti radios have only one functional Ethernet port. In this case an external switch must be used the provide vlan separation of the WAN and LAN traffic.
There is an operational tunnel server on the Usery mesh system. If anyone would like to install the tunnel client software on appropriate hardware I would be happy to setup an account for a connection to this server. You will need a moderate speed (256K+) Internet connection with a small router that will allow a single IP address on your network to receive and forward traffic to a particular TCP port number. Most home routers can do this.