Changing subnet mask to /23 from /24 on local network

Ryan Mendoza asked:

I have a 255.255.255.0 subnet mask (/24) can I change the subnet mask to 255.255.254.0 (/23) and not affect the hosts? The hosts are hard coded with no DHCP in this scope. Will I have to change the network settings for each host after I change this?

My answer:


The purpose of the prefix (and the deprecated netmask) is to define which part of the address space is on link. If a host has the wrong prefix configured, it will not be able to reach all of the addresses on that link (example). So you will need to reconfigure every host which has had its address and prefix manually configured. I recommend you take this opportunity to undo the mistakes of the past and institute some sort of centralized IP address management, or at least a DHCP server.


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