This is a quick post to document an issue with the UAG if you have an array and you are using an external load balncer and therefore do not have the Forefront UAG integrated load balancing enabled.
What I initially tried to do was use the same IP addresses for my HTTP redirect trunk as my HTTPS trunk, so I had an HTTPS trunk ‘Trunk1’ already configured listening on public interface 192.168.0.1 and I was trying to configure the UAG to redirect HTTP traffic, listening on the same IP address 192.168.0.1.
Not asking a lot I thought? Unfortunately this configuration cannot be actiavted if you are using a UAG array and external load balancer and you will get the error message ‘Trunk cannot be activated due to the following: Invalid Internal IP address. Please choose a different IP.’
You have to configure separate IP addresses for your HTTP trunks, even if they are only redirecting traffic to your HTTPS trunks.
I ended up adding 192.168.0.11 to my public interface network adapter (Dont add another network adapter, just add an IP address on the existing adapter) and reconfigured my HTTP trunk to listen on 192.168.0.11 and redirect all traffic to Trunk1 on 192.168.0.1.
As most Enterprises will be using an external load balancer this issue should come up in your enterprise environment.
This is caveat is documented at the bottom of this Technet article.