Networking All-in-One For Dummies. Doug LoweЧитать онлайн книгу.
chapters of Book 2.
What Is the Internet?
The Goliath of all computer networks, the Internet links hundreds of millions of computer users throughout the world. Strictly speaking, the Internet is a network of networks. It consists of hundreds of thousands of separate computer networks, all interlinked, so that a user on any of those networks can reach out and potentially touch a user on any of the other networks. This network of networks connects more than a billion computers to each other. (That’s right, billion with a b.)
One of the official documents (RFC 2026) of the Internet Engineering Task Force (IETF) defines the Internet as “a loosely organized international collaboration of autonomous, interconnected networks.” Broken down piece by piece, this definition encompasses several key aspects of what the Internet is:
Loosely organized: No single organization has authority over the Internet. As a result, the Internet is not highly organized. Online services, such as America Online or MSN, are owned and operated by individual companies that control exactly what content appears on the service and what software can be used with the service. No one exercises that kind of control over the Internet. As a result, you can find just about any kind of material imaginable on the Internet. No one guarantees the accuracy of information that you find on the Internet, so you have to be careful as you work your way through the labyrinth.
International: Nearly 200 countries are represented on the Internet, from Afghanistan to Zimbabwe. JUST HOW BIG IS THE INTERNET?Because the Internet is not owned or controlled by any one organization, no one knows how big the Internet really is. Several organizations do attempt to periodically determine the size of the Internet, including the Internet Systems Consortium (ISC), which completed its last survey in January 2019 and found that well over a billion host computers are connected to the Internet. The first year the ISC did the survey (1993), it found only 1.3 million host computers. It passed 10 million hosts in 1996, 100 million hosts in 2000, and edged over 1 billion hosts in 2014.Unfortunately, no one knows how many actual users are on the Internet. Each host can support a single user — or in the case of domains, hundreds of thousands or perhaps even millions of users. No one really knows.In fact, the ISC gave up on trying to count the number of hosts on the Internet. The January 2019 survey was its last. If you’re interested, you can check its historical survey data at www.isc.org/network/survey.
Collaboration: The Internet exists only because many different organizations cooperate to provide the services and support needed to sustain it. For example, much of the software that drives the Internet is open source software that’s developed collaboratively by programmers throughout the world, who constantly work to improve the code.
Autonomous: The Internet community respects that organizations that join the Internet are free to make their own decisions about how they configure and operate their networks. Although legal issues sometimes boil up, for the most part, each player on the Internet operates independently.
Interconnected: The whole key to the Internet is the concept of interconnection, which uses standard protocols that enable networks to communicate with each other. Without the interconnection provided by the TCP/IP protocol, the Internet would not exist.
Networks: The Internet would be completely unmanageable if it consisted of half a billion individual users, all interconnected. That’s why the Internet is often described as a network of networks. Most individual users on the Internet don’t access the Internet directly. Instead, they access the Internet indirectly through another network, which may be a LAN in a business or academic environment, or a dialup or broadband network provided by an Internet service provider (ISP). In each case, however, the users of the local network access the Internet via a gateway IP router.The Internet is composed of several distinct types of networks: Government agencies, such as the Library of Congress and the White House; military sites (did you ever see War Games or any of the Terminator movies?); educational institutions, such as universities and colleges (and their libraries); businesses, such as Microsoft and IBM; ISPs, which allow individuals to access the Internet; and commercial online services, such as America Online and MSN.
A Little Internet History
The Internet has a fascinating history, if such things interest you. There’s no particular reason why you should be interested in such things, of course, except that a superficial understanding of how the Internet got started may help you to understand and cope with the way this massive computer network exists today. So here goes.
The Internet traces its beginnings back to a small network called ARPANET, built by the Department of Defense in 1969 to link defense installations. ARPANET soon expanded to include not only defense installations but universities as well. In the 1970s, ARPANET was split into two networks: one for military use (renamed MILNET) and the original ARPANET (for nonmilitary use). The two networks were connected by a networking link called IP — the Internet protocol — so called because it allowed communication between two networks.
The good folks who designed IP had the foresight to realize that soon, more than two networks would want to be connected. In fact, they left room for tens of thousands of networks to join the game, which is a good thing because it wasn’t long before the Internet began to take off.
By the mid-1980s, ARPANET was beginning to reach the limits of what it could do. Enter the National Science Foundation (NSF), which set up a nationwide network designed to provide access to huge supercomputers, those monolithic computers used to discover new prime numbers and calculate the orbits of distant galaxies. The supercomputers were never put to much use, but the network that was put together to support the supercomputers — NSFNET — was used. In fact, NSFNET replaced ARPANET as the new backbone for the Internet.
Then, out of the blue, it seemed as if the whole world became interested in the Internet. Stories about it appeared in Time and Newsweek. Any company that had “dot com” in its name practically doubled in value every month. Al Gore claimed he invented the Internet. The Net began to grow so fast that even NSFNET couldn’t keep up, so private commercial networks got into the game. The size of the Internet nearly doubled every year for most of the 1990s. Then, in the first few years of the millennium, the growth rate slowed a bit. However, the Internet still seems to be growing at the phenomenal rate of about 30 to 50 percent per year, and who knows how long this dizzying rate of growth will continue.
TCP/IP Standards and RFCs
The TCP/IP protocol standards that define how the Internet works are managed by the IETF. However, the IETF doesn’t impose standards. Instead, it simply oversees the process by which ideas are developed into agreed-upon standards.
An Internet standard is published in the Request for Comments (RFC) document. When a document is accepted for publication, it is assigned an RFC number by the IETF. The RFC is then published. After it’s published, an RFC is never changed. If a standard is enhanced, the enhancement is covered in a separate RFC.
Thousands of RFCs are available from the IETF website (www.ietf.org). The oldest RFC is RFC 0001, published in April 1969. It describes how the host computers communicated with each other in the original ARPANET. As of this writing, the most recent proposed standard is RFC 8892, entitled “Guidelines and Registration Procedures for Interface Types and Tunnel Types.”
Not all RFCs represent Internet standards. The following paragraphs summarize the various types of RFC documents:
Internet Standards Track: This type of RFC represents an Internet standard. Standards Track RFCs have one of three maturity levels, as described in Table 2-1. An RFC enters circulation with Proposed Standard status but may be elevated