I have deployed a couple of Profile Manager instances where the Apple Push Notification Service (APNs) was reachable at install, but due to some over zealous network administration, connectivity was lost along the way.
The big issue with this is that as a fairly silent failure, it may take a minute to troubleshoot why changes aren’t pushing to devices. If you have your Profile Manager (or other onsite MDM) instance under monitoring however, you can check for reachability at intervals, and have the troubleshooting done for you.
Thus, I have added my APNS reachability script to OSX-Monitoring-Tools. It can be used to ensure that monitored systems can see and connect to Apple’s APNS provider servers, and that clients can connect to receive notifications within the network.