由上图可知，当数据包大小改为2000后数据报被分成2片。 11. Print out the first fragment of the fragmented IP datagram. What information in the IP header indicates that the datagram been fragmented? What information in the IP header indicates whether this is the first fragment versus a latter fragment? How long is this IP datagram?
由数据报首部的flag不为0可知数据报被分片，flag为0时表示这是最后一片，offset为0表示这是第一片。这个IP数据报的长度为1480+500+20=2000字节。
12. Print out the second fragment of the fragmented IP datagram. What information in the IP header indicates that this is not the first datagram fragment? Are the more fragments? How can you tell?
答：从这片的片内偏移量不为0可以看出这不是第一片，又因为这片的标志位已
经是0所以它已经是最后一片。
13. What fields change in the IP header between the first and second fragment?Now find the first ICMP Echo Request message that was sent by your computer after you changed the Packet Size in pingplotter to be 3500. 截图如下：
答：改变的头部字段有：数据报总长度 ，标识，片偏移，首部检验和等
14. How many fragments were created from the original datagram?
答：由上图可知是3个。
15. What fields change in the IP header among the fragments?
答：IP数据报首部改变的有：数据报总长度 ，标识，片偏移，首部检验和。 四、实验总结
通过本次实验，在详细分析IP协议，IP数据报的过程中，进一步对IP协议以及IP数据报有了更深的理解。更加细致深入地了解了IP数据报首部的各个字段的含义，明白了IP分片的具体情况。