Subnetting a Company Network

Currently we have subnet mask 255.255.255.0 Ip range 192.168.10.1-255

If I want to subnet this network can I use the following:

Subnet Mask 255.255.252.0

Ip ranges
192.168.10.8 1-255
192.168.10.9 1-255
192.168.10.10 1-255
192.168.10.11 1-255

Is it this simple?????

I realize I need to update router, firewall, servers, etc...

 

Well, subnetmask 255.255.252.0 is 11111111.11111111.11111100.00000000.
Your current IP's are 198.168.10.xxx, which is 11000000.10101000.00001010.xxx

So your network now include IP's with the third octet 00001000 (8), 00001001 (9), 00001010 (10), and 00001011 (11) as hosts on the same network.

So your IP's are now:
192.168.8-11.1-255

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Alternately, you could change your IP's to 192.168.0-3.1-255 with a 22-bit subnet mask.

However, you should arguably change your subnet to 255.255.240.0 or 255.255.0.0. That simply makes the math easier in my head. Your network becomes either 192.168.0-127.1-255 or 192.168.0-255.1-255.

Unless there's some reason you want to have a small pool of possible IP's.