Apache: The Definitive Guide, 3rd Edition

What to Know About TCP/IP

To understand the substance of this book, you need a modest knowledge of what TCP/IP is and what it does. You’ll find more than enough information in Craig Hunt and Robert Bruce Thompson’s books on TCP/IP,^[6] but what follows is, we think, what is necessary to know for our book’s purposes.

TCP/IP (Transmission Control Protocol/Internet Protocol) is a set of protocols enabling computers to talk to each other over networks. The two protocols that give the suite its name are among the most important, but there are many others, and we shall meet some of them later. These protocols are embodied in programs on your computer written by someone or other; it doesn’t much matter who. TCP/IP seems unusual among computer standards in that the programs that implement it actually work, and their authors have not tried too much to improve on the original conceptions.

TCP/IP is generally only used where there is a network.^[7] Each computer on a network that wants to use TCP/IP has an IP address , for example, 192.168.123.1.

There are four parts in the address, separated by periods. Each part corresponds to a byte, so the whole address is four bytes long. You will, in consequence, seldom see any of the parts outside the range 0 -255.

Although not required by the protocol, by convention there is a dividing line somewhere inside this number: to the left is the network number and to the right, the host number. Two machines on the same physical network — usually a local ...