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<html lang="zh"><head><title>网络是怎样连接的</title><meta charset="utf-8"/><link rel="preconnect" href="https://fonts.googleapis.com"/><link rel="preconnect" href="https://fonts.gstatic.com"/><link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=IBM Plex Mono&family=Noto Serif Simplified Chinese:wght@400;700&family=Source Sans Pro:ital,wght@0,400;0,600;1,400;1,600&display=swap"/><meta name="viewport" content="width=device-width, initial-scale=1.0"/><meta property="og:title" content="网络是怎样连接的"/><meta property="og:description" content="本书以探索之旅的形式，从在浏览器中输入网址开始，一路追踪了到显示出网页内容为止的整个过程，以图配文，讲解了网络的全貌，并重点介绍了实际的网络设备和软件是如何工作的。目的是帮助读者理解网络的本质意义，理解实际的设备和软件，进而熟练运用网络技术。同时，专设了“网络术语其实很简单”专栏，以对话的形式介绍了一些网络术语的词源，颇为生动有趣。本书图文并茂，通俗易懂，非常适合计算机、网络爱好者及相关从业人员阅读。 ..."/><meta property="og:image" content="https://wiki.7wate.com/static/og-image.png"/><meta property="og:width" content="1200"/><meta property="og:height" content="675"/><link rel="icon" href="../../../static/icon.png"/><meta name="description" content="本书以探索之旅的形式，从在浏览器中输入网址开始，一路追踪了到显示出网页内容为止的整个过程，以图配文，讲解了网络的全貌，并重点介绍了实际的网络设备和软件是如何工作的。目的是帮助读者理解网络的本质意义，理解实际的设备和软件，进而熟练运用网络技术。同时，专设了“网络术语其实很简单”专栏，以对话的形式介绍了一些网络术语的词源，颇为生动有趣。本书图文并茂，通俗易懂，非常适合计算机、网络爱好者及相关从业人员阅读。 ..."/><meta name="generator" content="Quartz"/><link href="../../../index.css" rel="stylesheet" type="text/css" spa-preserve/><link href="https://cdnjs.cloudflare.com/ajax/libs/KaTeX/0.16.9/katex.min.css" rel="stylesheet" type="text/css" spa-preserve/><script src="../../../prescript.js" type="application/javascript" spa-preserve></script><script type="application/javascript" spa-preserve>const fetchData = fetch("../../../static/contentIndex.json").then(data => data.json())</script></head><body data-slug="Personal/Book/计算机/网络是怎样连接的"><div id="quartz-root" class="page"><div id="quartz-body"><div class="left sidebar"><h2 class="page-title"><a href="../../..">🪴 X·Eden</a></h2><div class="spacer mobile-only"></div><div class="search"><button class="search-button" id="search-button"><p>搜索</p><svg role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 19.9 19.7"><title>Search</title><g class="search-path" fill="none"><path stroke-linecap="square" d="M18.5 18.3l-5.4-5.4"></path><circle cx="8" cy="8" r="7"></circle></g></svg></button><div id="search-container"><div id="search-space"><input autocomplete="off" id="search-bar" name="search" type="text" aria-label="搜索些什么" placeholder="搜索些什么"/><div id="search-layout" data-preview="true"></div></div></div></div><button class="darkmode" id="darkmode"><svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" id="dayIcon" x="0px" y="0px" viewBox="0 0 35 35" style="enable-background:new 0 0 35 35" xml:space="preserve" aria-label="暗色模式"><title>暗色模式</title><path d="M6,17.5C6,16.672,5.328,16,4.5,16h-3C0.672,16,0,16.672,0,17.5 S0.672,19,1.5,19h3C5.328,19,6,18.328,6,17.5z M7.5,26c-0.414,0-0.789,0.168-1.061,0.439l-2,2C4.168,28.711,4,29.086,4,29.5 C4,30.328,4.671,31,5.5,31c0.414,0,0.789-0.168,1.06-0.44l2-2C8.832,28.289,9,27.914,9,27.5C9,26.672,8.329,26,7.5,26z M17.5,6 C18.329,6,19,5.328,19,4.5v-3C19,0.672,18.329,0,17.5,0S16,0.672,16,1.5v3C16,5.328,16.671,6,17.
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<ul>
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<li><strong>书名</strong>：《网络是怎样连接的》</li>
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<li><strong>作者</strong>： 户根勤</li>
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<li><strong>分类</strong>： 计算机-计算机综合</li>
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<li><strong>ISBN</strong>：9787115441249</li>
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<li><strong>出版社</strong>：人民邮电出版社</li>
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</ul>
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<h2 id="概述">概述<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#概述" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
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<p>本书以探索之旅的形式，从在浏览器中输入网址开始，一路追踪了到显示出网页内容为止的整个过程，以图配文，讲解了网络的全貌，并重点介绍了实际的网络设备和软件是如何工作的。目的是帮助读者理解网络的本质意义，理解实际的设备和软件，进而熟练运用网络技术。同时，专设了“网络术语其实很简单”专栏，以对话的形式介绍了一些网络术语的词源，颇为生动有趣。本书图文并茂，通俗易懂，非常适合计算机、网络爱好者及相关从业人员阅读。</p>
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<h2 id="划线">划线<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#划线" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
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<blockquote>
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<p>本书以探索之旅的形式，从在浏览器中输入网址开始，一路追踪了到显示出网页的内容为止的整个过程，以图配文，讲解了网络的全貌，并重点介绍了实际的网络设备和软件是如何工作的。</p>
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</blockquote>
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<blockquote>
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<p>从在浏览器中输入网址，到屏幕上显示出网页的内容，在这个只有几秒钟的过程中，很多硬件和软件都在各自的岗位上相互配合完成了一系列的工作。</p>
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</blockquote>
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<blockquote>
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<p>虽然Web服务器在收到订单数据之后和销售系统一起对订单进行实际处理的操作很复杂，但其实浏览器和Web服务器之间的交互却很简单，概括如下。</p>
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</blockquote>
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<blockquote>
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<p>不过，没有文件名，服务器怎么知道要访问哪个文件呢？其实，我们会在服务器上事先设置好文件名省略时要访问的默认文件名。这个设置根据服务器不同而不同，大多数情况下是index.html或者default.htm之类的文件名。</p>
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</blockquote>
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<blockquote>
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<p>像前面这样省略文件名时，服务器就会访问/dir/index.html或者/dir/default.htm。</p>
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</blockquote>
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<blockquote>
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<p>生成HTTP消息之后，接下来我们需要委托操作系统将消息发送给Web服务器。尽管浏览器能够解析网址并生成HTTP消息，但它本身并不具备将消息发送到网络中的功能，因此这一功能需要委托操作系统来实现[插图]。</p>
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</blockquote>
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<blockquote>
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<p>这就是我们平常经常见到的IP地址格式，但仅凭这一串数字我们无法区分哪部分是网络号，哪部分是主机号。</p>
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</blockquote>
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<blockquote>
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<p>网络号和主机号连起来总共是32比特</p>
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</blockquote>
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<blockquote>
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<p>IP地址的长度为32比特，也就是4字节，相对地，域名最短也要几十个字节，最长甚至可以达到255字节。换句话说，使用IP地址只需要处理4字节的数字，而域名则需要处理几十个到255个字节的字符，这增加了路由器的负担，传送数据也会花费更长的时间[插图]。</p>
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</blockquote>
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<blockquote>
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<p>Class在最早设计DNS方案时，DNS在互联网以外的其他网络中的应用也被考虑到了，而Class就是用来识别网络的信息。不过，如今除了互联网并没有其他的网络了，因此Class的值永远是代表互联网的IN</p>
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</blockquote>
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<blockquote>
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<p>创建套接字阶段</p>
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</blockquote>
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<blockquote>
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<p>只要指定了事先规定好的端口号，就可以连接到相应的服务器程序的套接字。</p>
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</blockquote>
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<blockquote>
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<p>将网络包发送给通信对象的操作就是由IP来负责的。此外，IP中还包括ICMP[插图]协议和ARP[插图]协议。ICMP用于告知网络包传送过程中产生的错误以及各种控制消息，ARP用于根据IP地址查询相应的以太网MAC地址[插图]。</p>
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</blockquote>
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<blockquote>
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<p>在协议栈看来，要发送的数据就是一定长度的二进制字节序列而已。其次，协议栈并不是一收到数据就马上发送出去，而是会将数据存放在内部的发送缓冲区中，并等待应用程序的下一段数据。</p>
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</blockquote>
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<blockquote>
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<p>图3.4 双绞线对噪声的抑制（a）通过两根信号线的缠绕抵消外源性噪声；（b）通过改变节距抑制内源性噪声。</p>
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</blockquote>
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<blockquote>
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<p>[插图]</p>
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</blockquote>
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<blockquote>
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<p>从设备整体的转发能力来看，交换机要高于集线器。</p>
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</blockquote>
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<blockquote>
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<p>因为路由器是基于IP设计的，而交换机是基于以太网设计的[插图]。</p>
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</blockquote>
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<blockquote>
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<p>路由器判断下一个转发目标的方法如下。●如果路由表的网关列内容为IP地址，则该地址就是下一个转发目标。●如果路由表的网关列内容为空，则IP头部中的接收方IP地址就是下一个转发目标。路由器也会使用ARP来查询下一个转发目标的MAC地址。</p>
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</blockquote>
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<blockquote>
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<p>规定某些地址是用于内网的，这些地址叫作私有地址，而原来的固定地址则叫作公有地址[插图]。</p>
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</blockquote>
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<blockquote>
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<p>距离的不同和路由的维护方式，就是互联网与家庭、公司网络之间最主要的两个不同点。</p>
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</blockquote>
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<blockquote>
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<p>用户名和密码通过RADIUS[插图]协议从RAS[插图]发送到认证服务器，认证服务器校验这些信息是否正确。当确认无误后，认证服务器会返回IP地址等配置信息，并将这些信息下发给用户（图4.17②-3）。用户的计算机根据这些信息配置IP地址等参数，完成TCP/IP收发网络包的准备工作，接下来就可以发送TCP/IP包了</p>
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</blockquote>
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<blockquote>
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<p>这个路由信息交换的过程是由路由器自动完成的，这里使用的机制称为BGP[插图]。</p>
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</blockquote>
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<h2 id="笔记">笔记<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#笔记" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
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<blockquote>
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<p>像浏览器、邮件等一般的应用程序都是使用TCP收发数据的，而像DNS查询等收发较短的控制数据的时候则使用UDP。</p>
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</blockquote>
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<p>💭 TCP打电话，UDP写信</p>
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<blockquote>
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<p>部署防火墙[插图]。防火墙的作用类似于海关，它只允许发往指定服务器的指定应用程序的网络包通过，从而屏蔽其他不允许通过的包。</p>
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</blockquote>
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<p>💭 防火墙类似于海关</p>
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<blockquote>
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<p>除了使用多台功能相同的Web服务器分担负载之外，还有另外一种方法，就是将整个系统按功能分成不同的服务器[插图]，如Web服务器、数据库服务器。缓存服务器就是一种按功能来分担负载的方法。</p>
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</blockquote>
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<p>💭 水平扩展，垂直扩展</p>
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<h2 id="书评">书评<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#书评" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2>
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<h2 id="点评">点评<a role="anchor" aria-hidden="true" tabindex="-1" data-no-popover="true" href="#点评" class="internal"><svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M10 13a5 5 0 0 0 7.54.54l3-3a5 5 0 0 0-7.07-7.07l-1.72 1.71"></path><path d="M14 11a5 5 0 0 0-7.54-.54l-3 3a5 5 0 0 0 7.07 7.07l1.71-1.71"></path></svg></a></h2></article><hr/><div class="page-footer"></div></div><div class="right sidebar"><div class="graph"><h3>关系图谱</h3><div class="graph-outer"><div id="graph-container" data-cfg="{"drag":true,"zoom":true,"depth":1,"scale":1.1,"repelForce":0.5,"centerForce":0.3,"linkDistance":30,"fontSize":0.6,"opacityScale":1,"showTags":true,"removeTags":[],"focusOnHover":false}"></div><button id="global-graph-icon" aria-label="Global Graph"><svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px" viewBox="0 0 55 55" fill="currentColor" xml:space="preserve"><path d="M49,0c-3.309,0-6,2.691-6,6c0,1.035,0.263,2.009,0.726,2.86l-9.829,9.829C32.542,17.634,30.846,17,29,17
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