Whew! You covered a lot of ground in this hour to ensure that you have a grasp of network topologies and protocols. You should have a good foundation for the next several chapters in which you'll learn the specifics of computer and network hardware and software. With the theory presented in this hour and the knowledge of network hardware that's coming up, you'll have the basic knowledge to design your network.
Q What are the actual breakdowns of Class A, B, and C addresses?
There are actually limitations on which numbers can be assigned to each address class. These limitations are specified in RFC 796 and later related RFC documents. The breakdowns are as follows:
- Class A addresses range from roughly 1.X.X.X to 126.X.X.X, where the Xs represent any number from 0 to 255.
- Class B addresses range from 128.0.X.X to 191.255.X.X.
- Class C addresses range from 192.0.0.X to 223.255.255.X.
IP address numbers are assigned through the Internet Assigned Numbers Authority (IANA) through Network Solutions, Inc., in Virginia.
What happens if I need a Class C address, but have to use the addresses in a WAN in which routers pass data between networks at different locations?
Believe it or not, this is not a problem. In an attempt to allocate IP addresses as efficiently as possible, the designers of IP made provisions for subnetting, which means breaking a given address space (such as a full Class C address of 256 IP addresses) into smaller units. Data is routed between the subnets according to the way the network is divided.
For example, consider a Class C network with the network number 192.168.10.0. This network has 256 IP addresses ranging from 192.168.10.0 to 192.168.10.255. Suppose that you have 25 users in separate locations. The first subnet covers addresses 192.168.10.1 through 192.168.10.26 (remember that the 0 address is usually reserved for the network address itself). The next network's rightmost number ranges from 26 to 51, and so forth. This arrangement enables a network to appear to be one network192.168.10.0to anyone outside the network (in other words, on the Internet) but actually to be many smaller networks.