Practical UNIX and Internet Security, 3rd Edition

IP: The Internet Protocol

The Internet Protocol is the glue that holds together modern computer networks. IP specifies the way that messages are sent from computer to computer; it essentially defines a common “language” that is spoken by every computer stationed on the Internet.

This section describes IPv4, the fourth version of the Internet Protocol, which has been used on the Internet since 1982. IPv4 is universally used today, and will likely see continued use for many years to come. IPv5 was an experimental protocol that was never widely used. IPv6 is the newest version of the Internet Protocol. IPv6 provides for a dramatically expanded address space, built-in encryption, and plug-and-play Internet connectivity. As this book goes to press, IPv6 is largely being used on an experimental basis, although use of this new Internet Protocol is increasing. Nevertheless, we expect IPv4 to be the dominant protocol version for many years to come.

As we said earlier, at a very abstract level the Internet is similar to the phone network. However, looking more closely at the underlying protocols, we find that it is actually quite different. On the telephone network, each conversation is assigned a circuit (either a pair of wires or a channel on a multiplexed connection) that used for the duration of the telephone call. Whether you talk or not, the channel remains open until you hang up the phone.

On the Internet, the connections between computers are shared by all of the conversations. Data ...