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173.
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IP routing is a means of specifying and discovering paths in a TCP/IP network along which network data may be sent. Routing uses a set of <emphasis>routing tables</emphasis> to direct the forwarding of network data packets from their source to the destination, often via many intermediary network nodes known as <emphasis>routers</emphasis>. IP Routing is the principal mode of path discovery on the Internet. There are two primary forms of IP Routing: <emphasis>Static Routing</emphasis> and <emphasis>Dynamic Routing.</emphasis>
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IP 路由是在 TCP/IP 网络上为可能发送的网络数据指明或发现路径。路由使用一组<emphasis>路由表</emphasis>来指示网络数据包从源地址转发到目的地，经常是通过许多叫做路由器的网络节点做中转。IP 路由是 Internet 上路径发现的主要方式。IP 路由分为两种形式：<emphasis>静态路由</emphasis> 和 <emphasis>动态路由</emphasis>。
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Translated and reviewed by
姚渺波
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Located in
C/network-applications.xml:298(para)
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174.
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Static routing involves manually adding IP routes to the system's routing table, and this is usually done by manipulating the routing table with the <application>route</application> command. Static routing enjoys many advantages over dynamic routing, such as simplicity of implementation on smaller networks, predictability (the routing table is always computed in advance, and thus the route is precisely the same each time it used), and low overhead on other routers and network links due to the lack of a dynamic routing protocol. However, static routing does present some disadvantages as well. For example, static routing is limited to small networks and does not scale well. Static routing also fails completely to adapt to network outages and failures along the route due to the fixed nature of the route.
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静态路由包含向系统路由表中手工添加的 IP 路由，一般是通过 <application>route</application> 命令来向路由表手工添加的。静态路由与动态路由相比有许多优点，如在小网络中实施简单，有可预测性 (路由表总是事先算好，因此路由在每次使用时都相当一致)，在其它路由器和网络链路处理上比动态路由协议开销小。然而，静态路由也有一些缺点。如静态路由只限于小网络而且不能很好地进行调整。静态路由由于路由固定的特性，因此根本无法根据路由来适应网络中断和故障。
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Translated and reviewed by
姚渺波
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Located in
C/network-applications.xml:307(para)
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175.
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Dynamic Routing depends on large networks with multiple possible IP routes from a source to a destination and makes use of special routing protocols, such as the Router Information Protocol (RIP), which handle the automatic adjustments in routing tables that make dynamic routing possible. Dynamic routing has several advantages over static routing, such as superior scalability and the ability to adapt to failures and outages along network routes. Additionally, there is less manual configuration of the routing tables, since routers learn from one another about their existence and available routes. This trait also eliminates the possibility of introducing mistakes in the routing tables via human error. Dynamic routing is not perfect, however, and presents disadvantages such as heightened complexity and additional network overhead from router communications, which does not immediately benefit the end users, but still consumes network bandwidth.
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动态路由有赖于从一个源到目的有多条可用 IP 路由的大型网络，利用特定的路由协议，如路由信息协议 (RIP)，可以自动调整路由表以生成可能的动态路由。动态路由相对静态路由有几个优点,如拥有较大的伸缩性和能根据网络路由来适应网络中断和故障。另外，几乎无须手工配置路由表，因为路由器可以相互学到其他已有并且可用的路由器。这一特性也消除了由于人为错误而在路由表中引入错误的可能。然而，动态路由也并不完美，其表现出来的缺点如相当复杂以及由于路由器通讯所带来的额外的网络开销，并不能使最终用户由此获益，并却一直消耗着网络带宽。
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Translated and reviewed by
姚渺波
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Located in
C/network-applications.xml:317(para)
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176.
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TCP and UDP
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TCP 和 UDP
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Translated and reviewed by
姚渺波
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Located in
serverguide/C/network-config.xml:782(title)
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177.
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TCP is a connection-based protocol, offering error correction and guaranteed delivery of data via what is known as <emphasis>flow control</emphasis>. Flow control determines when the flow of a data stream needs to be stopped, and previously sent data packets should to be re-sent due to problems such as <emphasis>collisions</emphasis>, for example, thus ensuring complete and accurate delivery of the data. TCP is typically used in the exchange of important information such as database transactions.
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TCP 是一个基于连接的协议，提供纠错并通过 <emphasis>流量控制</emphasis> 来传输数据。流量控制决定什么时间一个数据流需要停止，例如在出现诸如 <emphasis>冲突</emphasis> 等问题时重发先前发送的数据包，以确保完整和准确的数据传输。TCP 常用于重要信息的交换，如数据库传输。
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Translated and reviewed by
姚渺波
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TCP 是一个基于连接的协议，提供纠错并通过 <emphasis>流量控制</emphasis> 来确保数据的送达。流量控制决定像什么时候需要停止一个数据流，以及在出现诸如 <emphasis>冲突</emphasis> 等问题时重发先前发送的数据包，以确保完整和准确的数据传输。TCP 常用于重要信息的交换，如数据库事务。
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Suggested by
Ihnus Qcshz
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Located in
serverguide/C/network-config.xml:783(para)
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178.
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The User Datagram Protocol (UDP), on the other hand, is a <emphasis>connectionless</emphasis> protocol which seldom deals with the transmission of important data because it lacks flow control or any other method to ensure reliable delivery of the data. UDP is commonly used in such applications as audio and video streaming, where it is considerably faster than TCP due to the lack of error correction and flow control, and where the loss of a few packets is not generally catastrophic.
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另一方面，用户数据报协议 (UDP) 是一个 <emphasis>无连接</emphasis> 协议，很少用于重要数据的传输，因为缺乏流量控制或其他一些确保可靠数据传输的方法。UDP 常用在如音视频流这样的应用程序，由于它缺少纠错和流控，因此相对于 TCP 来说更快，而且丢失少量包通常也不会造成灾难性的后果。
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Translated and reviewed by
姚渺波
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Located in
serverguide/C/network-config.xml:791(para)
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179.
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ICMP
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ICMP
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Translated and reviewed by
姚渺波
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Located in
serverguide/C/network-config.xml:801(title)
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180.
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The Internet Control Messaging Protocol (ICMP) is an extension to the Internet Protocol (IP) as defined in the Request For Comments (RFC) #792 and supports network packets containing control, error, and informational messages. ICMP is used by such network applications as the <application>ping</application> utility, which can determine the availability of a network host or device. Examples of some error messages returned by ICMP which are useful to both network hosts and devices such as routers, include <emphasis>Destination Unreachable</emphasis> and <emphasis>Time Exceeded</emphasis>.
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Internet 控制消息协议是在Request For Comments (RFC) #792 中定义的，是对网际协议 (IP) 的一个扩充。支持的网络包包括控制、错误和信息的消息。ICMP 常被用在诸如判断一台网络主机或设备可用性的 <application>ping</application> 工具这样的网络应用程序。在网络主机和设备如路由器之间使用 ICMP 所返回的错误消息示例包括 <emphasis>Destination Unreachable</emphasis> 和 <emphasis>Time Exceeded</emphasis>。
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Translated and reviewed by
姚渺波
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Located in
serverguide/C/network-config.xml:802(para)
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181.
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Daemons
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守护程序
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Translated and reviewed by
姚渺波
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Located in
serverguide/C/network-config.xml:812(title)
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182.
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Daemons are special system applications which typically execute continuously in the background and await requests for the functions they provide from other applications. Many daemons are network-centric; that is, a large number of daemons executing in the background on an Ubuntu system may provide network-related functionality. Some examples of such network daemons include the <emphasis>Hyper Text Transport Protocol Daemon</emphasis> (httpd), which provides web server functionality; the <emphasis>Secure SHell Daemon</emphasis> (sshd), which provides secure remote login shell and file transfer capabilities; and the <emphasis>Internet Message Access Protocol Daemon</emphasis> (imapd), which provides E-Mail services.
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守护程序是特殊的系统应用程序，一般常驻在后台并等待来自其他应用程序请求其所提供的功能。许多守护程序都是网络中心；在 Ubuntu 系统后台执行的许多守护程序都可以提供网络的相关功能。这些网络守护程序包括 <emphasis>超文本传输协议守护程序</emphasis> (httpd)，用于提供网站服务器功能；<emphasis>Secure SHell 守护程序</emphasis> (sshd)，用于提供安全远程登录 shell 和文件传输功能；<emphasis>Internet Message Access Protocol 守护程序</emphasis> (imapd)，用于提供 E-Mail 服务。
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Translated and reviewed by
姚渺波
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| In upstream: |
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守护程序是特殊的系统应用程序，一般常驻在后台并等待来自其他应用程序请求其所提供的功能。许多守护程序都是面向网络的；也就是说，在 Ubuntu 系统后台执行的许多守护程序都可以提供网络的相关功能。这些网络守护程序包括 <emphasis>超文本传输协议守护程序</emphasis> (httpd)，用于提供web服务器功能；<emphasis>Secure SHell 守护程序</emphasis> (sshd)，用于提供安全远程登录 shell 和文件传输功能；<emphasis>Internet Message Access Protocol 守护程序</emphasis> (imapd)，用于提供 E-Mail 服务。
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Suggested by
Ihnus Qcshz
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Located in
serverguide/C/network-config.xml:813(para)
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