I need more IP addresses. Can I change my mask from 192.168.x.0/24 to /16? Why not?

I'm using 192.168.x.x and have exhausted the IP pool. Since 192.168.0.0/16 is all private, why can't I just change the mask to 255.255.0.0 and start allocating out 192.168.x+1.x IPs?

Edit: I realise that this would preclude me from linking to any other 192.168.x.0/24 networks

Of course you can use a /16, or /23, /22 etc. if you want, I know we have at least a couple of /23's in place and it works fine. Obviously you'll have to alter your netmasks everywhere and especially on your router/s but this is very commonly done.

I personally wouldn't go the whole hog and use a /16, as you say it could cause problems if you're using 192.168.x.y addresses elsewhere, so just choose a /23 or /22 and that should last you a long while.

Nothing stops you doing this - with private address ranges, such as the 192.168.0.0/16 netblock and the 10.0.0.0/8 netblock. Technically you could use non private address space - especially behind an address translating firewall - but it's rude and may become a massive nuisance.

192.16.0.0/24 is a common address range to use. But that's all. People commonly use /24 address blocks, because it neatly maps to the IP address range octets. A netmask is a bit mask that says the first (24 in this case) bits are 'network' and the remainder are 'local subnet'.

That basically means 192.168.0.0/24 is 192.168.0.1 - 192.168.0.255. Another common convention is to adopt '.1' as the gateway, and '.255' as the broadcast. Drop your netmask to 23 bits though, and you double the size of your subnet - 192.168.0.1 - 192.168.1.255. Each bit doubles the size. So whilst a /24 contains 256 addresses (8 'bits worth') - a /16 leaves 16 bits for host - 65,535 addresses.

The same is true of /16 and /8 - they map nicely to the octets of the dotted quad IP format. They are known as class A, class B and class C address ranges and once upon a time, when the internet was a much smaller place, that's all there was. Which is why you'll see a lot of (established) organisations have a /16 or class B, despite - probably - not using most of it on the public Internet.