UDP 协议简介

haoayou · 发表于 2024-7-10 18:16:53

马上注册，结交更多好友，享用更多功能，让你轻松玩转社区。

您需要登录才可以下载或查看，没有账号？立即注册

×

<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">UDP 协议简介<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">UDP是一个简单的面向数据报的传输层协议：进程的每个输出操作都正好产生一个 UDP数据报，并组装成一份待发送的IP数据报。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">这与面向流字符的协议不同，如 TCP，应用程序产生的全体数据与真正发送的单个IP数据报可能没有什么联系。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">UDP不提供可靠性：它把应用程序传给IP层的数据发送出去，但是并不保证它们能到达目的地。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">应用程序必须关心IP数据报的长度。如果它超过网络的 MTU，那么就要对IP数据报进行分片。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">UDP/IP 的报文结构如下图所示：<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462721755972966554775.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="84" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462721755972966554775.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462723815375394997058.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="82" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462723815375394997058.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● 端口号表示发送进程和接收进程。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● TCP端口号与UDP端口号是相互独立的。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● 尽管相互独立，如果TCP和UDP同时提供某种知名服务，两个协议通常选择相同的端口号。这纯粹是为了使用方便，而不是协议本身的要求。(DNS)<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● UDP长度字段指的是UDP首部和UDP数据的字节长度。该字段的最小值为      8字节。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462731999630258393789.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="135" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462731999630258393789.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● UDP检验和是覆盖UDP首部和UDP数据。IP首部的校验和，它只覆盖IP的首部<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● UDP的检验和是可选的，而TCP的检验和是必需的。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● IP计算校验和和UDP计算校验和之间存在不同的地方。首先，      UDP数据报的长度可以为奇数字节，但是检验和算法是把若干个 16 bit字相加。解决方法是必要时在最后增加填充字节      0，这只是为了检验和的计算（也就是说，可能增加的填充字节不被传送）。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">● UDP数据报和TCP段都包含一个1      2字节长的伪首部，它是为了计算检验和而设置的。伪首部包含IP首部一些字段。其目的是让UDP两次检查数据是否已经正确到达目的地（例如，IP没有接收地址不是本主机的数据报，以及      IP没有把应传给另一高层的数据报传给 UDP）。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">上图中，我们特地举了一个奇数长度的数据报例子，因而在计算检验和时需要加上填充字节。注意，UDP数据报的长度在检验和计算过程中出现两次。如果检验和的计算结果为 0，则存入的值为全1（65535），这在二进制反码计算中是等效的。如果传送的检验和为0，说明发送端没有计算检验和。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">如果发送端没有计算检验和而接收端检测到检验和有差错，那么 UDP数据报就要被悄悄地丢弃。不产生任何差错报文（当 IP层检测到IP首部检验和有差错时也这样做）。 UDP检验和是一个端到端的检验和。它由发送端计算，然后由接收端验证。其目的是为了发现UDP首部和数据在发送端到接收端之间发生的任何改动。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">Python 实现UDP协议<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">Python利用Socket模块来实现UDP协议。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">UDP Socket Server的示例程序：<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462740038700976332858.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="211" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462740038700976332858.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">UDP Socket Client的示例程序：<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462742373476945030913.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="150" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462742373476945030913.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">运行UDP Socket Client程序并开启抓包<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462746054182372189489.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="189" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462746054182372189489.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462746716689302798847.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="119" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462746716689302798847.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">从抓取到的数据包可以看到：<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">1、没有会话建立的过程。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">2、数据并没有确认。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">3、应用的每一次操作，网络上对应一个数据包。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">4、服务器端没有开启侦听对应的UDP端口，就会自动发送ICMP的差错报文给发送端。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">对发送UDP报（红色框中的1号）和响应报（红色框中的2号）进行详细分析如下图：<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462749478581592792588.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="126" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462749478581592792588.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">两种Python 发送UDP数据方式<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">方式一：Socket发送<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462753739513222974498.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="120" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462753739513222974498.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">方式二：Scapy sr1发送<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"> <p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);"><a target="_blank" href="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462758173254863598445.png" style="padding: 0px; margin: 0px; color: rgb(50, 50, 50); text-decoration-line: none; background-color: transparent; border: none; outline: none !important;"><img width="230" height="70" src="https://www.ad.siemens.com.cn/club/bbs/upload/image/20231103/6383462758173254863598445.png" style="padding: 0px; margin: 0px; border: 0px; vertical-align: middle;"/></a><p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">两种方式的差别：<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">方式一是把UDP数据转交给驱动程序处理，数据长度超了MTU后，数据的分片由驱动来自动实现，劣势是不能指定发送的网卡接口。<p style="padding: 0px; margin-top: 0px; margin-bottom: 0px; font-family: "Noto Sans SC", "Microsoft YaHei", ΢��ź�, -apple-system, BlinkMacSystemFont, "segoe ui", Roboto; color: rgb(51, 51, 51); font-size: 12px; text-wrap: wrap; background-color: rgb(255, 255, 255);">方式二是通过Scapy发送数据，数据不转交驱动程序，所以有分片需求时，不能被自动实现分片功能，优势是可以选择发送的接口网卡。

UDP 协议简介

马上注册，结交更多好友，享用更多功能，让你轻松玩转社区。

回复

浏览过的版块