Minimum Requirement: The minimum Requirement is that TCP port 443 is open. Some firewall/proxy rules only allow for SSL traffic over port 443. You will need to make sure that non-web traffic can also pass over this port.
Better Experience: In addition to the minimum requirements being met, we also recommend that UDP port 3478 is open.
Best Experience: For the best possible experience, we recommend that UDP ports 1025 - 65535 be open.