rfc1935.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                      J. Quarterman
Request For Comments: 1935                               S. Carl-Mitchell
Category: Informational                                               TIC
                                                               April 1996


                     What is the Internet, Anyway?

Status of This Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Copyright (c) 1994  TIC

        From Matrix News, 4(8), August 1994
        Permission is hereby granted for redistribution of this article
        provided that it is redistributed in its entirety, including
        the copyright notice and this notice.
        Contact: [e-mail], [phone], fax: [phone].
        http://www.tic.com/mids, gopher://gopher.tic.com/11/matrix/news
        A shorter version of this article appeared in MicroTimes.

Introduction

   We often mention the Internet, and in the press you read about the
   Internet as the prototype of the Information Highway; as a research
   tool; as open for business; as not ready for prime time; as a place
   your children might communicate with (pick one) a. strangers, b.
   teachers, c. pornographers, d. other children, e. their parents; as
   bigger than Poland; as smaller than Chicago; as a place to surf; as
   the biggest hype since Woodstock; as a competitive business tool; as
   the newest thing since sliced bread.

   A recent New York Times article quoting one of us as to the current
   size of the Internet has particularly stirred up quite a ruckus.  The
   exact figures attributed to John in the article are not the ones we
   recommended for such use, but the main point of contention is whether
   the Internet is, as the gist of the article said, smaller than many
   other estimates have said.  Clearly lots of people really want to
   believe that the Internet is very large.  Succeeding discussion has
   shown that some want to believe that so much that they want to count
   computers and people that are probably *going to be* connected some
   time in the future, even if they are not actually connected now.  We
   prefer to talk about who is actually on the Internet and on other
   networks now.  We'll get back to the sizes of the various networks
   later, but for now let's discuss a more basic issue that is at the



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   heart of much confusion and contention about sizes: what is the
   Internet, anyway?

Starting at the Center

   For real confusion, start trying to get agreement on what is part of
   the Internet:  NSFNET?  CIX?  Your company's internal network?
   Prodigy?  FidoNet?  The mainframe in accounting?  Some people would
   include all of the above, and perhaps even consider excluding
   anything politically incorrect.  Others have cast doubts on each of
   the above.

   Let's start some place almost everyone would agree is on the
   Internet.  Take RIPE, for example.  The acronym stands for European
   IP Networks.  RIPE is a coordinating group for IP networking in
   Europe.  (IP is the Internet protocol, which is the basis of the
   Internet.  IP has a suite of associated protocols, including the
   Transmission Control Protocol, or TCP, and the name IP, or sometimes
   TCP/IP, is often used to refer to the whole protocol suite.) RIPE's
   computers are physically located in Amsterdam.  The important feature
   of RIPE for our purposes is that you can reach RIPE (usually by using
   its domain, ripe.net) from just about anywhere anyone would agree is
   on the Internet.

   Reach it with what?  Well, just about any service anyone would agree
   is related to the Internet.  RIPE has a WWW (World Wide Web) server,
   a Gopher server, and an anonymous FTP server.  So they provide
   documents and other resources by hypertext, menu browsing, and file
   retrieval.  Their personnel use client programs such as Mosaic and
   Lynx to access other people's servers, too, so RIPE is a both
   distributor and a consumer of resources via WWW, Gopher, and FTP.
   They support TELNET interfaces to some of their services, and of
   course they can TELNET out and log in remotely anywhere they have
   personal login accounts or someone else has an anonymous TELNET
   service such a library catalog available.  They also have electronic
   mail, they run some mailing lists, and some of their people read and
   post news articles to USENET newsgroups.

   WWW, Gopher, FTP, TELNET, mail, lists, and news:  that's a pretty
   characteristic set of major Internet services.  There are many more
   obscure Internet services, but it's pretty safe to say that an
   organization like RIPE that is reachable with all these services is
   on the Internet.

   Reachable from where?  Russia first connected to the Internet in
   1992.  For a while it was reachable from networks in the Commercial
   Internet Exchange (CIX) and from various other networks, but not from
   NSFNET, the U.S. National Science Foundation network.  At the time,



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   some people considered NSFNET so important that they didn't count
   Russia as reachable because it wasn't accessible through NSFNET.
   Since there are now several other backbone networks in the U.S. as
   fast (T3 or 45Mbps) as NSFNET, and routing through NSFNET isn't very
   restricted anymore, few people would make that distinction anymore.
   So for the moment let's just say reachable through NSFNET or CIX
   networks, and get back to services.

Looking at Firewalls

   Many companies and other organizations run networks that are
   deliberately firewalled so that their users can get to servers like
   those at ripe.net, but nobody outside the company network can get to
   company hosts.  A user of such a network can thus use WWW, Gopher,
   FTP, and TELNET, but cannot supply resources through these protocols
   to people outside the company.  Since a network that is owned and
   operated by a company in support of its own operations is called an
   enterprise network, let's call these networks enterprise IP networks,
   since they typically use the Internet Protocol (IP) to support these
   services.  Some companies integrate their enterprise IP networks into
   the Internet without firewalls, but most do use firewalls, and those
   are the ones that are of interest here, since they're the ones with
   one-way access to these Internet services.  Another name for an
   enterprise IP network, with or without firewall, is an enterprise
   Internet.

   For purposes of this distinction between suppliers and consumers, it
   doesn't matter whether the hosts behind the firewall access servers
   beyond the firewall by direct IP and TCP connections from their own
   IP addresses, or whether they use proxy application gateways (such as
   SOCKS) at the firewall.  In either case, they can use outside
   services, but cannot supply them.

   So for services such as WWW, Gopher, FTP, and TELNET, we can draw a
   useful distinction between supplier or distributor computers such as
   those at ripe.net and consumer computers such as those inside
   firewalled enterprise IP networks.  It might seem more obvious to say
   producer computers and consumer computers, since those would be more
   clearly paired terms.  However, the information distributed by a
   supplier computer isn't necessarily produced on that computer or
   within its parent organization.  In fact, most of the information on
   the bigger FTP archive servers is produced elsewhere.  So we choose
   to say distributors and consumers.  Stores and shoppers would work
   about as well, if you prefer.

   Even more useful than discussing computers that actually are
   suppliers or consumers right now may be a distinction between
   supplier-capable computers (not firewalled) and consumer-capable



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   computers (firewalled).  This is because a computer that is not
   supplying information right now may be capable of doing so as soon as
   someone puts information on it and tells it to supply it.  That is,
   setting up a WWW, Gopher, or FTP server isn't very difficult; much
   less difficult than getting corporate permission to breach a
   firewall.  Similarly, a computer may not be able to retrieve
   resources by WWW, Gopher, at the moment, since client programs for
   those services usually don't come with the computer or its basic
   software, but almost any computer can be made capable of doing so by
   adding some software.  In both cases, once you've got the basic IP
   network connection, adding capabilities for specific services is
   relatively easy.

   Let's call the non-firewalled computers the core Internet, and the
   core plus the consumer-capable computers the consumer Internet.  Some
   people have referred to these two categories as the Backbone Internet
   and the Internet Web.  We find the already existing connotations of
   "Backbone" and "Web" confusing, so we prefer core Internet and
   consumer Internet.

   It's true that many companies with firewalls have one or two
   computers carefully placed at the firewall so that they can serve
   resources.  Company employees may be able to place resources on these
   servers, but they can't serve resources directly from their own
   computers.  It's rather like having to reserve space on a single
   company delivery truck, instead of owning one yourself.  If you're
   talking about companies, yes, the company is thus fully on the core
   Internet, yet its users aren't as fully on the Internet as users not
   behind a firewall.

   If you're just interested in computers that can distribute
   information (maybe you're selling server software), that's a much
   smaller Internet than if you're interested in all the computers that
   can retrieve such information for their users (maybe you have
   information you want to distribute).  A few years ago it probably
   wouldn't have been hard to get agreement that firewalled company
   networks were a different kind of thing than the Internet itself.
   Nowadays, firewalls have become so popular that it's hard to find an
   enterprise IP network that is not firewalled, and the total number of
   hosts on such consumer-capable networks is probably almost as large
   as the number on the supplier-capable core of the Internet.  So many
   people now like to include these consumer-capable networks along with
   the supplier-capable core when discussing the Internet.

   Some people claim that you can't measure the number of consumer-
   capable computers or users through measurements taken on the Internet
   itself.  Perhaps not, but you can get an idea of how many actual
   consumers there are by simply counting accesses to selected servers



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   and comparing the results to other known facts about the accessing
   organizations.  And there are other ways to get useful information
   about consumers on the Internet, including asking them.

Mail, Lists, and News

   But what about mail, lists, and news?  We carefully left those out of
   the discussion of firewalls, because almost all the firewalled
   networks do let these communications services in and out, so there's
   little useful distinction between firewalled and non-firewalled
   networks on the basis of these services.  That's because there's a
   big difference between these communications services and the resource
   sharing (TELNET, FTP) and resource discovery (Gopher, WWW) services
   that firewalls usually filter.  The communications services are
   normally batch, asynchronous, or store-and-forward.  These
   characterizations mean more or less the same thing, so pick the one
   you like best.  The point is that when you send mail, you compose a
   message and queue it for delivery.  The actual delivery is a separate
   process; it may take seconds or hours, but it is done after you
   finish composing the message, and you normally do not have to wait
   for the message to be delivered before doing something else.  It is
   not uncommon for a mail system to batch up several messages to go
   through a single network link or to the same destination and then
   deliver them all at once.  And mail doesn't even necessarily go to
   its final destination in one hop; repeated storing at an intermediate
   destination followed by forwarding to another computer is common;
   thus the term store-and-forward.  Mailing lists are built on top of
   the same delivery mechanisms as regular electronic mail.  USENET news
   uses somewhat different delivery mechanisms, but ones that are also
   typically batch, asynchronous, and store-and-forward.  Because it is
   delivered in this manner, a mail message or a news article is much
   less likely to be a security problem than a TELNET, FTP, Gopher, or
   WWW connection.  This is why firewalls usually pass mail, lists, and
   news in both directions, but usually stop incoming connections of
   those interactive protocols.

   Because WWW, Gopher, TELNET, and FTP are basically interactive, you
   need IP or something like it to support them.  Because mail, lists,
   and news are asynchronous, you can support them with protocols that
   are not interactive, such as UUCP and FidoNet.  In fact, there are
   whole networks that do just that, called UUCP and FidoNet, among
   others.  These networks carry mail and news, but are not capable of
   supporting TELNET, FTP, Gopher, or WWW.  We don't consider them part
   of the Internet, since they lack the most distinctive and
   characteristic services of the Internet.

   Some people argue that networks such as FidoNet and UUCP should also
   be counted as being part of the Internet, since electronic mail is



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   the most-used service even on the core, supplier-capable Internet.
   They further argue that the biggest benefit of the Internet is the
   community of discussion it supports, and mail is enough to join that.
   Well, if mail is enough to be on the Internet, why is the Internet
   drawing such attention from press and new users alike?  Mail has been
   around for quite a while (1972 or 1973), but that's not what has made
   such an impression on the public.  What has is the interactive
   services, and interfaces to them such as Mosaic.  Asynchronous
   networks such as FidoNet and UUCP don't support those interactive
   services, and are thus not part of the Internet.  Besides, if being
   part of a community of discussion was enough, we would have to also
   include anyone with a fax machine or a telephone.  Recent events have
   demonstrated that all readers of the New York Times would also have
   to be included.  With edges so vague, what would be the point in
   calling anything the Internet?  We choose to stick with a definition
   of the Internet as requiring the interactive services.

   Some people argue that anything that uses RFC-822 mail is therefore
   using Internet mail and must be part of the Internet.  We find this
   about as plausible as arguing that anybody who flies in a Boeing 737
   is using American equipment and is thus within the United States.
   Besides, there are plenty of systems out there that use mail but not
   RFC-822.