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31.4.2 IP地址和DNS名称
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31.4.2 IP地址和DNS名称
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h3 style='margin-top:8.15pt;margin-right:0cm;FTEL:8.15pt;margin-left:
0cm'><a FTEL="_Toc535009265"></a><a FTEL="_Toc507815537"><span lang=EN-US>31.4.2
IP</span></a><span style='font-family:黑体'>地址和</span><span lang=EN-US>DNS</span><span
style='font-family:黑体'>名称</span></h3>
<p class=MsoNormal><span style='font-family:宋体'>在</span><span lang=EN-US>Internet</span><span
style='font-family:宋体'>上，服务器和客户机都由</span><span lang=EN-US>IP</span><span
style='font-family:宋体'>地址或主机名</span><span lang=EN-US>(</span><span
style='font-family:宋体'>也称作</span><span lang=EN-US>DNS</span><span
style='font-family:宋体'>名称</span><span lang=EN-US>)</span><span
style='font-family:宋体'>标识。通常，主机名是在</span><span lang=EN-US>Web</span><span
style='font-family:宋体'>浏览器的窗口中键入的友好名称，例如</span><span lang=EN-US>www.wrox.com</span><span
style='font-family:宋体'>或</span><span lang=EN-US>www.microsoft.com</span><span
style='font-family:宋体'>等。另一方面，</span><span lang=EN-US>IP</span><span
style='font-family:宋体'>地址是计算机用于互相标识的标识符，它实际上是用于确保</span><span lang=EN-US>Web</span><span
style='font-family:宋体'>请求和响应到达相应机器的地址。计算机甚至可以有多个</span><span lang=EN-US>IP</span><span
style='font-family:宋体'>地址。</span></p>
<p class=MsoNormal><span style='font-family:宋体'>为了使这些主机名发挥作用，首先必须发送一个网络请求，把主机名翻译成</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址，翻译工作由一个或几个</span><span
lang=EN-US>DNS</span><span style='font-family:宋体'>服务器完成。</span></p>
<p class=MsoNormal><span lang=EN-US>DNS</span><span style='font-family:宋体'>服务器中保存的一个表把主机名映射为它知道的所有计算机的</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址，以及用于其他</span><span
lang=EN-US>DNS</span><span style='font-family:宋体'>服务器在该表中查找它不知道的主机名的其他</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址。本地计算机至少要知道一个</span><span
lang=EN-US>DNS</span><span style='font-family:宋体'>服务器。网络管理员在计算机启动时配置该信息。</span></p>
<p class=MsoNormal><span style='font-family:宋体'>在发送请求之前，计算机首先应要求</span><span
lang=EN-US>DNS</span><span style='font-family:宋体'>服务器指出与键入的主机名相对应的</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址。找到正确的</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址后，计算机就可以定位请求，并通过网络发送它。这些工作一般都在后台发生，用户仅浏览</span><span
lang=EN-US>Web</span><span style='font-family:宋体'>即可。</span></p>
<h4 style='FTEL:21.45pt'><span lang=EN-US>1. </span><span
style='font-family:黑体'>用于</span><span lang=EN-US>IP</span><span
style='font-family:黑体'>地址的</span><span lang=EN-US>.NET</span><span
style='font-family:黑体'>类</span></h4>
<p class=MsoNormal><span lang=EN-US>.NET Framework</span><span
style='font-family:宋体'>提供了许多能够帮助寻找</span><span lang=EN-US>IP</span><span
style='font-family:宋体'>地址和主机信息的类。</span></p>
<p class=MsoNormal><span lang=EN-US>(1) IPAddress</span><span style='font-family:
宋体'>类</span></p>
<p class=MsoNormal><span lang=EN-US>IPAddress</span><span style='font-family:
宋体'>类代表</span><span lang=EN-US>IP</span><span style='font-family:宋体'>地址。地址本身可以作为</span><span
lang=EN-US>Address</span><span style='font-family:宋体'>属性，使用</span><span
lang=EN-US>ToString()</span><span style='font-family:宋体'>方法可以把</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址转化为用小数点隔开的十进制格式。此外，</span><span
lang=EN-US>IPAddress</span><span style='font-family:宋体'>也执行静态的</span><span
lang=EN-US>Parse()</span><span style='font-family:宋体'>方法，这个方法的作用与</span><span
lang=EN-US>ToString()</span><span style='font-family:宋体'>方法正好相反，把小数点隔开的十进制字符串转化为</span><span
lang=EN-US>IP</span><span style='font-family:宋体'>地址。</span></p>
<p class=2 style='margin-top:8.15pt;margin-right:0cm;FTEL:0cm;
margin-left:21.45pt;FTEL:.0001pt;FTEL:18.45pt'><span
lang=EN-US>IPAddress ipAddress = IPAddress.Parse("234.56.78.9");</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>long
address = ipAddress.Address; </span></p>
<p class=2 style='margin-top:0cm;margin-right:0cm;FTEL:8.15pt;
margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>string ipString = ipAddress.ToString();
</span></p>
<p class=MsoNormal><span style='font-family:宋体'>在上面的示例中，</span><span
lang=EN-US>long</span><span style='font-family:宋体'>整型数</span><span lang=EN-US>address</span><span
style='font-family:宋体'>的值为</span><span lang=EN-US>156121322</span><span
style='font-family:宋体'>，字符串</span><span lang=EN-US>ipString</span><span
style='font-family:宋体'>的值为文本“</span><span lang=EN-US>234.56.78.9</span><span
style='font-family:宋体'>”。</span></p>
<p class=MsoNormal><span lang=EN-US>IPAddress</span><span style='font-family:
宋体'>还提供了许多静态的常量字段，以返回特殊的</span><span lang=EN-US>IP</span><span
style='font-family:宋体'>地址。例如，</span><span lang=EN-US>Loopback</span><span
style='font-family:宋体'>地址允许机器给它自己发送消息，而</span><span lang=EN-US>Broadcast</span><span
style='font-family:宋体'>允许多路传送到本地网络上。</span></p>
<p class=2 style='margin-top:8.15pt;margin-right:0cm;FTEL:0cm;
margin-left:21.45pt;FTEL:.0001pt;FTEL:18.45pt'><span
lang=EN-US>// The following line will set loopback to "127.0.0.1". </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>//
the loopback address indicates the local host. </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>string
loopback = IPAddress.Loopback.ToString();</span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US> </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>//
The following line will set broadcast address to "255.255.255.255". </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>//
the broadcast address is used to send a message to all machines on </span></p>
<p class=2 style='margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>//
the local network. </span></p>
<p class=2 style='margin-top:0cm;margin-right:0cm;FTEL:8.15pt;
margin-left:21.45pt;FTEL:18.45pt'><span lang=EN-US>string broadcast =
IPAddress.Broadcast.ToString();</span></p>
<p class=MsoNormal><span lang=EN-US>(2) IPHostEntry</span><span
style='font-family:宋体'>类</span></p>
<p class=MsoNormal><span lang=EN-US>IPHostEntry</span><span style='font-family:
宋体'>类用于封装与某台主机相关的信息。通过这个类的</span><span lang=EN-US>HostName</span><span
style='font-family:宋体'>属性</span><span lang=EN-US>(</span><span
style='font-family:宋体'>这个属性返回一个字符串</span><span lang=EN-US>)</span><span
style='font-family:宋体'>，可以使用主机名称；通过</span><span lang=EN-US>AddressList</span><span
style='font-family:宋体'>属性返回一个</span><span lang=EN-US>IPAddress</span><span
style='font-family:宋体'>对象的数组。下一个示例</span><span lang=EN-US>DNSResolver</span><span
style='font-family:宋体'>将使用</span><span lang=EN-US>IPHostEntry</span><span
style='font-family:宋体'>类。</span></p>
<p class=MsoNormal><span lang=EN-US>(3) Dns</span><span style='font-family:
宋体'>类</span></p>
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