Microsoft Skype Business Server Issue

Ok, I have helped a client setup a Microsoft Skype Business Server on an LTM. I used the iApp for both Lync and Skype. The Skype seems to work better. I have gotten almost all of the services communicating through the F5 with no issues. Did have to make a few tweaks but nothing big. Here is my question and issue. How do you get desktop sharing to work form internal to external and external to internal. They are able to share internal to internal and external to external.

 

We have gone through all the MS documentation and all the firewall rules are in place and the servers are setup correctly.

 

It is setup with a 2 tier LB setup - 1 external for Edge Services and the other Internal for Web Services / AV / Reverse Proxy.

 

Thanks for any help provided.

 

Matt