Class A, Class C, no class? Does it matter?

[Chromaverse]

I recently visited a foreign LAN that had a subnet 100.200.100.0 with netmask 255.255.255.0. There were less than ten devices on the LAN, with no more than 20 devices ever planned to be on the network. I thought that didn't seem right.

I don't know a whole lot about subnetting, but I do know that a "large LAN" needing 254 hosts could use the popular 192.168.0.0/24 subnet, which falls into a class C network addressing scheme. It seems to me like the person who set up this foreign network just picked a bunch of random numbers (100, 200, 100) to make up their subnet, rather than picking a network that falls into a classed IP addressing scheme.

Because of the subnet mask 255.255.255.0 (24 mask bits), wouldn't 100.200.100.0/24 be neither class A nor class C? To be a class A network, wouldn't the subnet mask need to be 255.0.0.0 (8 mask bits), and to be a class C, the first octet would need fall into the range 192-223?

Does any of this even matter? Class C, Class B, Class A that is. Can a network administrator just pick any numbers they want to create a simple LAN? Are network classes just an optional specification that can be safely ignored?

 

[nickbits]

What matters is that the network is setup to use one of the private ip address ranges.

100.200. is not in one of those ranges.

See http://pcsupport.about.com/od/termsp/g/private-ip-address.htm

 

[Railgun]

If they own it (or even if they don't) they can technically use whatever they want within their four walls.

 

[her209]

RFC 1918 reserves IP address ranges that are won't be routed on the public Internet and are, therefore, the preferred ranges, but the network engineer could use IP addresses outside of the private IP address ranges. It just becomes "confusing" when hosts actually need to get to the Internet space that uses those IP address range as well.

 

[serpretetsky]

Class A, Class C, no class? Does it matter?

No, it does no matter. CIDR has replaced classful routing. However, you can't pick whatever network addresses you want. You either choose private IP's, are you are assigned public ip's.