i've been asked to change my subnet mask on our network from a 255.255.0.0 to a 255.255.255.0 (we are using DHCP and are using windowsServer 2012). - this should not be an issue for the number of users, however i'm concerned what issues may occur from the change = will devices and their ability to connect become an issue? how to correct or possibly avoid issue? Another piece of this is - i was asked to reduce our ip range of “ x.x.80.2 to x.x.85.254“ to a range of “ x.x.80.2 to x.x.80.254“ again, this should not be an issue for the number of users and any reserved IP's are already in that range - but i'm wondering what issue could occur and how to correct. Will most issues be resolved from a DNS restart and power cycling of devices to force new ip's to be acquired? (i was also going to minimize the dhcp lease time before i attempt the change and restore it to its normal setting after successful completion ) ... any and all advise is very welcome - this is outside of my scope of expertise. i will also note: the place where i can change the scope (ip range) has a section indicating the subnet mask but its greyed out - does that indicate that the ip range change may update the subnet mask automatically (I can’t find another location to change the subnet mask itself ) ?? so many questions - thank you in advance for all advice provided.
*this was requested by our managed firewall team because we are having an issue creating a vpn tunnel between locations due to mismatched subnet masks that cannot communicate with each other.