Another factor that can block devices from connecting to the server is the DHCP
lease time. Basically in this case, after some time without active use of the
device, the network will unassign the IP address from the device and it will
become unreachable. This configuration is common in networks in order to save
connections and IPs.
This is extremely common for networks with a large number of devices. It drops devices that are not in use, to open room for the devices that are in use. It's an optimization strategy for enterprise networks. You can configure the timeout of the IP lease: this is the DHCP lease time.
After this time, any devices that are not in use will lose a valid internet connection and will not be able to be reached by the MDM server. You can test it: just send a command to the device and check the last update you receive from the MDM.
When you restart a device you are basically renewing your connection with the DHCP and for this reason the device may receive and act upon all pending commands. However, it’s nice to have in mind:
- If you hold the IP for too much time, when there’s a new iPad, an IP address will not be available for this specific device (because there’s no IP range available). On the other hand, if this time is too short, the iPad can lose its connection and will no longer reconnect.
With that in mind, our suggestion is to configure a subnet mask, to increase or decrease the IP range available. A majority of schools use /24 (254 hosts/not), but this amount must be calculated based on the number of devices in your institution.