We currently have a private IP subnet using the 192.168.1.0/24 range. We are running out of IP addresses and would like to extend this subnet, to something like 192.168.0.0/21.
Is it possible to do such change without significant downtime? if we first change the VLAN configuration on our switch to use the new netmask, will all the connected machines with the old configuration immediately break until we change their configuration? or will they continue to work as before but will only see the previous subnet, and not hosts with IPs on the extended subnet, and then we could gradually change the netmask on each host with no downtime except what's required for a local NIC restart?