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Chiyo Yuki 2025-09-09 16:55:05 +08:00
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**华东师范大学软件学院实验报告**
**一、实验目的**
1. 学会使用curl与wget指令
2. 学会通过Wireshark获取数据包
3. 了解协议层数据包的结构
4. 学会计算并分析协议开销
**二、实验内容与实验步骤**
1. 在控制台中输入"curl http://1st.moe/",并观察到"200 OK"
2. 启动Wireshark选择监听以太网并将捕获过滤器设置为tcp port
> 80关闭混杂模式并启用"enable network name resolution"选项
3. 关闭所有浏览器窗口后开始捕获
4. 重新在控制台输入"curl [**http://1st.moe/**](http://1st.moe/)"
5. 停止Wireshark捕获
**三、实验环境**
> B226机房电脑
**四、实验过程与分析**
1. 实验过程
1) 捕获内容如图所示
> ![](./images/Pictures/100000010000094B000002EADEAFEA2E.png){width="17.007cm"
> height="5.3cm"}
2. 1) 分析协议包的内容
> ![](./images/Pictures/10000001000003320000015C8A9E98EE.png){width="8.504cm"
> height="3.6cm"}![](./images/Pictures/100000010000032800000154F3640027.png){width="8.504cm"
> height="3.579cm"}![](./images/Pictures/100000010000032900000152B123680E.png){width="8.504cm"
> height="3.556cm"}![](./images/Pictures/100000010000033300000151977B0DF0.png){width="8.504cm"
> height="3.489cm"}
> 根据如上四张图片,可以发现各个协议所占的字节数为
+---------------------------------------+-------------+
| > 协议 | > 字节数 |
+---------------------------------------+-------------+
| > Ethernet (eth) | > 14 bytes |
+---------------------------------------+-------------+
| > Internet Protocol Version 6 (ipv6) | > 40 bytes |
+---------------------------------------+-------------+
| > Transmission Control Protocol (tcp) | > 20 bytes |
+---------------------------------------+-------------+
| > Hypertext Transfer Protocol (http) | > 128 bytes |
+---------------------------------------+-------------+
> 则包的结构大致如下
+-------------------+--------------------+------------+-------------+
| > eth | > ip | > tcp | > http |
+-------------------+--------------------+------------+-------------+
| > 14 bytes | > 40 bytes | > 20 bytes | > 128 bytes |
+-------------------+--------------------+------------+-------------+
| > Ethernet Header | > Ethernet Payload | | |
+-------------------+--------------------+------------+-------------+
| > IP Header | > IP Payload | | |
+-------------------+--------------------+------------+-------------+
3. 问题
1) 分析协议开销
> 一个GET本身的大小为128
> bytes而其相应产生的SYN、ACK请求也应算入其开销中。根据图片
> ![](./images/Pictures/10000001000004EE0000005E50C8B369.png){width="17.096cm"
> height="1.281cm"}
> 可以计算得出由于协议产生的总开销为86+74+(202-128)+74=308
> 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。
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
> 根据图片
> ![](./images/Pictures/10000001000004000000007864293250.png){width="17.096cm"
> height="2.009cm"}
> ![](./images/Pictures/1000000100000470000000F4B4E41AC7.png){width="17.096cm"
> height="3.667cm"}
> 可以直观看出ipv6对应的分解键为0x86ddtcp对应的分解键为6
5. 故障分析
> 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。
**五、实验结果总结**
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
+-------------------+--------------------+------------+-------------+
| > Eth | > ip | > tcp | > http |
+-------------------+--------------------+------------+-------------+
| > 14 bytes | > 40 bytes | > 20 bytes | > 128 bytes |
+-------------------+--------------------+------------+-------------+
| > Ethernet Header | > Ethernet Payload | | |
+-------------------+--------------------+------------+-------------+
| > IP Header | > IP Payload | | |
+-------------------+--------------------+------------+-------------+
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
3. 通过查询相关资料,了解开销、分解键等概念
**六、附录**
**无**