UM 2.3 - Adding Rule Error

Just set up UM 2.3 and got it connected to vCenter fine.  However, when I try and create rules for customer VMs, I get the error:

"The server cannot be contacted at this time"

There is a hardware firewall between UM and vCenter.  I opened ports 80 and 443 so that UM could talk to vCenter.  I'm thinking there are other ports required.  Does anyone have a list of firewall ports that UM 2.3 needs open?

Thanks!