Static ip addresses?

so we want to use the SE zone servers to sync time in our environment
However the firewall rules are working with IP addresses and not hostnames, so can I be sure that those 4 servers have always the same IP? If not then the firewall rules will stop working and sync will fail.

Hi, the servers in the pool are all provided by volunteers so could be anywhere in the world and appear and disappear without warning. I would have a look at the “Additional Notes” section here and consider whether the pool is appropriate for you. If you do decide to use the pool then you would need to allow NTP packets from any IP through your firewall.