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**华东师范大学软件学院实验报告**
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**一、实验目的**
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1. 学会使用curl与wget指令
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2. 学会通过Wireshark获取数据包
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3. 了解协议层数据包的结构
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4. 学会计算并分析协议开销
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**二、实验内容与实验步骤**
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1. 在控制台中输入"curl http://1st.moe/",并观察到"200 OK"
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2. 启动Wireshark,选择监听以太网,并将捕获过滤器设置为tcp port
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> 80,关闭混杂模式,并启用"enable network name resolution"选项
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3. 关闭所有浏览器窗口后开始捕获
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4. 重新在控制台输入"curl [**http://1st.moe/**](http://1st.moe/)"
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5. 停止Wireshark捕获
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**三、实验环境**
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> B226机房电脑
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**四、实验过程与分析**
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1. 实验过程
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1) 捕获内容如图所示
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> {width="17.007cm"
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> height="5.3cm"}
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2. 1) 分析协议包的内容
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> {width="8.504cm"
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> height="3.6cm"}{width="8.504cm"
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> height="3.579cm"}{width="8.504cm"
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> height="3.556cm"}{width="8.504cm"
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> height="3.489cm"}
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> 根据如上四张图片,可以发现各个协议所占的字节数为
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+---------------------------------------+-------------+
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| > 协议 | > 字节数 |
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+---------------------------------------+-------------+
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| > Ethernet (eth) | > 14 bytes |
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+---------------------------------------+-------------+
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| > Internet Protocol Version 6 (ipv6) | > 40 bytes |
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+---------------------------------------+-------------+
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| > Transmission Control Protocol (tcp) | > 20 bytes |
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+---------------------------------------+-------------+
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| > Hypertext Transfer Protocol (http) | > 128 bytes |
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+---------------------------------------+-------------+
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> 则包的结构大致如下
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+-------------------+--------------------+------------+-------------+
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| > eth | > ip | > tcp | > http |
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+-------------------+--------------------+------------+-------------+
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| > 14 bytes | > 40 bytes | > 20 bytes | > 128 bytes |
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+-------------------+--------------------+------------+-------------+
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| > Ethernet Header | > Ethernet Payload | | |
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+-------------------+--------------------+------------+-------------+
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| > IP Header | > IP Payload | | |
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+-------------------+--------------------+------------+-------------+
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3. 问题
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1) 分析协议开销
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> 一个GET本身的大小为128
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> bytes,而其相应产生的SYN、ACK请求也应算入其开销中。根据图片
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> {width="17.096cm"
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> height="1.281cm"}
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> 可以计算得出由于协议产生的总开销为86+74+(202-128)+74=308
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> bytes,从而计算得出比值约为0.4156,考虑到信息传输的稳定性,协议开销是值得的。
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4. 1) 以太网头部中哪一部分是解复用键并且告知它的下一个高层指的是IP,在这一包内哪一个值可以表示IP
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> 根据图片
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> {width="17.096cm"
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> height="2.009cm"}
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> {width="17.096cm"
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> height="3.667cm"}
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> 可以直观看出ipv6对应的分解键为0x86dd,tcp对应的分解键为6
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5. 故障分析
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> 在实验过程中出现了控制台有反馈但Wireshark没有捕获的情况,经排查后发现是由于控制台指令输入错误:误将http输入为https所致。
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**五、实验结果总结**
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1. 实验完成了对一个HTTP包的拆解与分析,其大体结构大致如下
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+-------------------+--------------------+------------+-------------+
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| > Eth | > ip | > tcp | > http |
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+-------------------+--------------------+------------+-------------+
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| > 14 bytes | > 40 bytes | > 20 bytes | > 128 bytes |
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+-------------------+--------------------+------------+-------------+
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| > Ethernet Header | > Ethernet Payload | | |
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+-------------------+--------------------+------------+-------------+
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| > IP Header | > IP Payload | | |
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+-------------------+--------------------+------------+-------------+
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2. 实验通过curl指令与Wireshark软件完成,在其中熟悉网络工具的使用,并体会到其强大之处
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3. 通过查询相关资料,了解开销、分解键等概念
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**六、附录**
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**无**
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