Using FaceTime and iMessage behind a firewall
For most networks configurations, FaceTime video calling, FaceTime audio calling, and iMessage will just work. If you are on a network that is behind a firewall, see below.
Note: FaceTime and iMessage may not be available in all countries or regions.
About firewalls
Your corporation or educational institution may use a firewall for increased security. Firewalls work by blocking certain Internet traffic from entering or leaving a network.
Internet traffic moves through a firewall based on service-identification numbers that are referred to as ports. Certain ports must be open for FaceTime and iMessage to work. Network administrators typically open a minimal set of network ports, allowing the traffic for approved applications to enter and leave the network while blocking other network traffic.
Ports to open
If the network router that you are connected to uses a firewall or security software to restrict Internet access, contact the network administrator and refer them to this article.
Enable port forwarding on the following ports to use FaceTime and iMessage on a restricted network.