[心平气和读经典]The TCP/IP Guide(003)

The TCP/IP Guide

[Page 43, 44]

Scope of The TCP/IP Guide | 本书的讨论范围

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The first step to dealing with a problem is recognizing that you have one. So, I have to come clean with you, my reader. I have a problem: an addiction to... detail. :-) Every time I set out to write about a particular protocol, technology or concept, I start with a modest goal regarding how much I want to write. I always begin knowing that I really need to control myself, to prevent my project from going on forever. But as I explore each subject, I learn more and more, and I start to say to myself things like..."this is important, I simply must include coverage for it" and... "if I am going to cover subject #1, I also should cover subject #2, because they are related". This is how I turned a six-month project into a multi-year ordeal.

处理问题的第一步是认识到你有一个问题。所以，读者朋友，我必须跟你说清楚。我有一个问题： 对深入细节上瘾。每当我着手写一个特定的协议、技术或概念时，我给自己设定一个适度的目标：打算写多少。我总是考虑需要如何控制自己，以防项目永远没有结项的那一天。但是，当我每探索一个主题时，学的东西越来越多，于是，我开始对自己说，"这很重要，必须有所涵盖"。如果要涵盖主题#1, 也必须涵盖主题#2, 因为它们具有相关性。这就是一个6个月的项目是如何被我变成了一个漫长的充满煎熬的多年项目的过程。

However, even though self-control in this area is a weakness for me, even I realized I could not possibly cover everything related to TCP/IP in this Guide. Consider that the TCP/IP suite contains dozens of protocols and technologies that have each had thick books written about them. I was willing to spend years on this project but not decades. :-) Thus, I had to limit the scope of this Guide somewhat, both to preserve what remains of my sanity and to spare you from having to wade through a ridiculously large document.

然而，在这个领域进行自我控制对我来说是一个弱点，我甚至意识到我不可能在这个指南中涵盖所有与TCP/IP相关的东西。考虑到TCP/IP包含了几十种协议和技术，讲解每一个协议和技术在市面上都存在者相关的大部头的书籍。于是我愿意花很多年在这一项目上，但不是几十年:-) 因此，我不得不对本指南的范围进行限制，既保留了我想努力传递的东西，又不让读者花了很大力气读完本书却发现这不过是一个荒谬的大文件。

Here are a few different points that will help explain decisions that I made to limit the scope of The TCP/IP Guide:

下面有几个不同的要点将有助于解释限制本指南的范围的决定是如何做出的：

• Theory versus Practice: This is primarily a reference resource on the TCP/IP protocol suite. The material here is designed to allow a student to learn the nuts and bolts of how TCP/IP works. I do discuss quite a number of "real-world" practical issues related to how TCP/IP internetworks operate, but this is not my primary focus here. If you want to really understand what TCP/IP is and what makes it work, you've come to the right place. If all you want is simple instructions on how to connect a few PCs together in your home using TCP/IP, this probably isn't the Guide for you. :-)

  理论v.s.实践： 本指南主要是TCP/IP协议的参考资料。这些资料旨在让学生了解TCP/IP工作原理的基本原理。我讨论了相当数量的与使用TCP/IP如何进行网络互联操作相关的"真实世界"中存在的实际问题，但这不是我讨论的重点。如果你想真正理解TCP/IP是什么，以及它是如何工作的，那么你就来对地方了。如果你想要的只是简单地说明如何用TCP/IP连接你家里的几台电脑，这很可能不是你想要的指南。:-)

• Current versus Future Protocols: Most of the emphasis in this Guide is on the present state of the art in TCP/IP. The suite is always changing, and there are constantly new protocols being written and revisions to existing protocols being published. I have not provided extensive coverage of technologies still in development, to try to keep the size of the Guide manageable, and to reduce the number of changes I will have to make to keep the material up-to-date.

  The one exception to this general rule of thumb is version 6 of the Internet Protocol. IPv6 represents a significant change to the core of how most of TCP/IP operates. While not universally deployed yet, IPv6 is sufficiently far along in its development that I feel any student of TCP/IP needs to know what it is and how it works, and understand its significance. Thus, I have included a detailed section describing it, and also mentioned how it impacts the operation of several other key protocols such as ICMP, DNS and DHCP.

  当前协议v.s.未来协议： 本指南中的大部分重点是TCP/IP前沿技术。TCP/IP总是在不断变化，并且不断有新的协议被加入和对现有协议进行修改。为了使本指南的范围保持可控，并减少为了保持材料更新而进行的更改的次数，于是我没有对正在开发中的技术进行广泛的讲解。

  既定的通用规则中有一个例外，那就是Internet协议的第6版。IPv6代表了大多数TCP/IP操作的核心的一个重大变化。虽然IPv6还没有得到普遍的部署，但它的发展还远远不够，我觉得任何一个TCP/IP的学生都需要知道它是什么以及它是如何工作的，并理解它的重要性。因此，我在本书中详细地描述了它，并提到了它是如何影响其他几个关键协议(如ICMP、DNS和DHCP)的操作的。

• Application Coverage: There are many thousands of different applications that run on TCP/IP internetworks, and I could not possibly hope to describe all of them. The scope of this Guide is limited to the most important, "classical" TCP/IP applications and application protocols, such as electronic mail, general file transfer and the World Wide Web.
  应用范围： 在TCP/IP网络上跑着成千上万个不同的应用，描述所有的应用是不可能的。本指南的范围仅限于最重要的经典的TCP/IP应用及应用协议，比如电子邮件，通用文件传输和万维网。
• TCP/IP versus The Internet: The TCP/IP protocol suite and the Internet are very closely related in many ways, as you will discover as you read this Guide. In fact, they are often tied together so much that it is hard to discuss one without the other. However, the Internet as a whole is an enormous subject, and trying to describe it in general terms would have substantially increased the size of this Guide. Thus, I describe Internet issues only within the context of explanations of TCP/IP technologies.

  For example, while I cover the World Wide Web in this Guide, I discuss its generalities only briefly. I focus my technical discussions on how the Hypertext Transfer Protocol (HTTP) that implements it works. I don't talk all about how to set up a Web site, or how to choose a Web browser, or any of those sorts of details. These are covered in a dazzling array of different books, papers and of course, Web sites. :-)

  TCP/IP v.s. Internet网: TCP/IP协议簇和Internet在许多方面都密切相关，您在阅读本指南时就会发现。事实上，他们往往是绑定在一起的，以至于很难讨论其中一个而不谈及另一个。然而，整个互联网是一个庞大的课题，试图笼统地描述它将大大增加本指南的规模。因此，我仅在解释TCP/IP技术的上下文中描述一下Internet问题。

  例如，当我在本指南之中描述万维网时，只简单地探讨一下它的共性。我将重点讨论超文本传输协议(HTTP)协议是如何实现和工作的。至于如何建一个网站，或者如何选择一个网络浏览器，或者任何这些细节，都不讨论。有关这些内容的介绍，到处充斥着琳琅满目的书籍、论文和网站。:-)

• Limited TCP/IP Security Coverage: Security is a very important and very large topic, especially in modern networking. This Guide does include a fairly detailed section on the operation of the IP Security protocols (IPSec), and also touches upon security issues in describing several other protocols and technologies. However, it is not specifically geared towards detailed discussions of security considerations. It is possible that in the future I will add more security-related information, but for now, if your primary interest is TCP/IP security matters, you will want to supplement this Guide with other materials.

  较少地涵盖TCP/IP安全：在现代网络中，安全是一个非常重要且很大的话题。本指南确实包含了关于IPSec操作的一个相当详细的章节，并且还涉及了描述几种其他协议和技术的安全问题。然而，并不是专门针对安全考虑的详细讨论。将来我可能会添加更多与安全相关的内容，但是目前来说，如果您的主要兴趣是TCP/IP安全问题，请使用其他材料来作为本指南的补充。

• Small Computer Orientation: In general terms, TCP/IP technologies can be used to connect together any types of devices that have the appropriate hardware and software. There are some issues, however, where explanations require me to focus on how specific types of underlying networks and devices work; this is especially true of some of my diagrams. In these cases, my preference has generally been to show how TCP/IP is used to connect together typical small computers such as PCs, Macintoshes and UNIX workstations, which are what most people use.

  讨论基于小型计算机： 一般说来，TCP/IP技术可以用来连接任何类型的设备，只要这些设备具备合适的硬件和软件。然而，有一些问题需要解释一下，因为我需要把重点放在特定类型的底层网络和设备上，尤其是我提供的一些图表。在这种情况下，我倾向于展示如何使用TCP/IP把小型设备连接在一起，例如个人电脑，Mac和Unix工作站，这些设备为大多数人所使用。