Good morning Calvin,
Here is a link to the Techzone article on Horizon Firewall ports
If you look under the section "Client Connections" you will see the ports/protocol for Client access to the components of Horizon.
Are these clients internal on your corporate network or external? I've had clients with firewalls between Client and connection server as well as Client and VDI clones.
Hope this helps and let us know if you have more questions