It seems that despite my previous experiences with TMG 2010, I still stumble when creating a TMG array. Here are some “notes to self”, which will hopefully stop me making the same mistakes next time
In this case I came to a project after the initial installation of the array and there was no dedicated intra-array network installed. I added a new NIC to each VM and configured the IP addressing, VLANs and routing, but could not get the intra-array network to ping, let alone talk to each other. So the lesson here is to set up the servers with their NICs before you install TMG - Microsoft recommend a dedicated intra-array network and every bit of experience I have with TMG arrays confirms that.
This is simple, the order I have found to work is:
Some people recommend the Private/Internal network first, then the Intra-array, but I have found that this order works better (anyone able to dispute this or give me a reason why it should be the other way?). The key thing is that the External Network (which should be your default Gateway) is last in the binding order, which brings me to the next point…
Add any static and persistant routes required and make sure you can access those networks before installing TMG. This allows you to get the routing right without the complication of TMG rules and firewalls.
Then, and only then, install TMG 🙂