From Apple's documentation (emphasis on the interesting bit added):
Push providers, iOS devices, and Mac computers are often behind firewalls. To send notifications, you will need to have TCP port 2195 open. To reach the feedback service, you will need to have TCP port 2196 open. Devices and computers connecting to the push service over Wi-Fi will need to have TCP port 5223 open.
The IP address range for the push service is subject to change; the expectation is that providers will connect by hostname rather than IP address. The push service uses a load balancing scheme that yields a different IP address for the same hostname. However, the entire 17.0.0.0/8 address block is assigned to Apple, so you can specify that range in your firewall rules.
17.0.0.0/8 is CIDR notation for 17.0.0.1 to 17.255.255.254.
