The full set of instructions for whilelisting Photons is:
The Particle device cloud is comprised of many servers running in different places around the world. We routinely start and stop servers automatically to meet demand, and during routine maintenance, and it would be difficult to commit to a range of stable IP addresses. Our domain device.spark.io is dynamically updated and regenerated to reflect what local servers are available for devices, and is the best way to get a list of local servers to approve, but it is subject to routine change.
One alternative is to whitelist all Photon devices by MAC address, allowing them to make outgoing TCP connections to port 5683 on any host.
If this is not possible, as of the time of writing this is the list of IP addresses. It is subject to change.
If a new server is added, and is blocked by your firewall, it will time out and try again using a different server, but this will increase the time it takes to connect to the cloud.