classes of ip addresses

Hi all, I'm studying for the A+ exams, and I ran accross some practice test questions regarding the classification of IP addresses (class A, class B, etc...). I can't seem to find an explanation in any of my books, or online. Could someone explain how IP addresses are classified? Any help would be appreciated.
-cracker

Bearing in mind it goes a lot deeper with classes of subnets, with subnetting and supernetting, here is a quick explanation:

You have 4 main classes. A, B, C and D.

As you know, IP addresses are split by .'s into 4 octets. These octets define what network the device belongs on, and which device it is on the network:

Class A subnets mean the first octet defines which network it belongs to, and the latter 3 defines which device it is (Host ID).

Example: As long as the first octet is the same, and the devices have a route to each other, it doesnt matter what the last 3 octets are. They will be able to communicate.

Class B are the same is the same as A except the first 2 octets are the network ID, so as long as the first 2 octets are the same they will communicate.

Class C, same, but the first 3 octets...

Class D is a special class, normally reserved for broadcast IP's. I.E 255.255.255.255.

Like I said there are variations to this when you get into subnetting and supernetting, but for the purpose of A+ you wont need to know that.

HTH a bit!

Regards

Hong

PS if anyone notices any inconsistencies or errors let me know...in quite a rush!

Looky here:

http://www.learntosubnet.com/

Ok' I think I've got it now. Thanks!
-cracker

Np :)