networking - Subnetting/Supernetting Configuration

I have an existing network. It looks like this.

Router LAN (192.168.0.1 /24) -> Switch (192.168.0.10 /24) -> Workstations (192.168.0.100 - 192.168.0.200 /24)

Our network has expanded and I need to have more hosts available.

The simplest way to do this is to change the router's inside interface subnet (/24) to a supernet (/23).

This will give me 192.168.0.0-192.168.1.254 instead of just 192.168.0.0-192.168.0.254.

That is exactly what I want.

My question is do I need to adjust the subnet masks on hosts on either the 192.168.0.0 /24 network or 192.168.1.0 /24 network or should they continue to work having only changed the subnet mask on the inside interface of the router?

The reason I'm confused is 192.168.0.0 /24 and 192.168.1.0 /24 are both part of 192.168.0.0 /23 so in my mind there is not a need to change the subnet masks of hosts in those smaller networks but having made the subnet mask change only to the inside interface of the router I am not able to communicate with a host with the static IP address 192.168.1.40.

Finally, I would like to know if I need to change the subnet mask on the hosts, the switches, or both.

Answer

If you do this, then yes, you will need to change the netmask of all the hosts connected to the network, otherwise you will get annoying problems like hosts in different networks not being able to communicate. The ethernet-level method of contacting a host differs according to whether the destination host is on the same network or not, the netmask is used to determine whether this is the case.

The good news is that it only applies to communication between hosts in different (old or new) parts of the network. You can change the netmask on the router, then on all of the hosts, and then start adding hosts in the new part of the network.

If reconfiguring all the hosts is cumbersome, I would add a second IP (192.168.1.1/24) to your router's inside interface. Communication between the two networks would (at least to some extent) go through the router's inside interface, so if you plan to have a massive amount of communication between hosts in your network you may not want that. You could instead add something bigger, like 172.16.0.0/16, and gradually move over your computers from the old network.

You might want to investigate DHCP, especially if some part of your hosts are user machines that usually do not need to be contacted.