通信网原理实验报告Ethernet and ARP(3)

d) Where in the ARP request does the “question” appear – the Ethernet address of the machine whose corresponding IP address is being queried?

Answer：The field “Target MAC address” is set to 00:00:00:00:00:00 to question the machine whose corresponding IP address (192.168.1.105) is being queried.

15. Now find the ARP reply that was sent in response to the ARP request.

a) How many bytes from the very beginning of the Ethernet frame does the ARP opcode field begin?

Answer：The ARP opcode field begins 20 bytes from the very beginning of the Ethernet frame.

－ 11 －

b) What is the value of the opcode field within the ARP-payload part of the Ethernet frame in which an ARP response is made?

Answer：The hex value for opcode field withing the ARP-payload part of the Ethernet frame is 2．

c) Where in the ARP message does the “answer” to the earlier ARP request appear – the IP address of the machine having the Ethernet address whose corresponding IP address is being queried?

Answer：The answer to the earlier ARP request appears in the”Sender MAC address” field, which contains the Ethernet address 00:d0:59:a9:3d:68 for the sender with IP address 192.168.1.1.

－ 12 －

16. What are the hexadecimal values for the source and destination addresses in the Ethernet frame containing the ARP reply message? Answer：The hex value for the source address is 00:06:25:da:af:73 and for the destination is 00:d0:59:a9:3d:68 .

17. Open the ethernet-ethereal-trace-1 trace file in

http://gaia.cs.umass.edu/wireshark-labs/wireshark-traces.zip. The first and second ARP packets in this trace correspond to an ARP request sent by the computer running Wireshark, and the ARP reply sent to the computer running Wireshark by the computer with the ARP-requested Ethernet address. But there is yet another computer on this network, as indiated by packet 6 – another ARP request. Why is there no ARP reply (sent in response to the ARP request in packet 6) in the packet trace? Answer：There is no reply in this trace, because we are not at the machine

－ 13 －

that sent the request. The ARP request is broadcast, but the ARP reply is sent back directly to the sender’s Ethernet address.

五、实验结论

1.CRC在WireShark中是不能被抓到的，原因是CRC在抓包之前已经被计算好。

2.ARP Request消息的Type字段值为1；ARP Replyt消息的Type字段值为2。

3.MAC address是唯一的。

4.清空ARP缓存时（ARP –d ）会出现如下的情况：

5.ARP –a 可以查看ARP缓存中的内容。 六、实验总结

通过这次实验，我对ARP协议有了进一步的理解，在实验过程中遇到了许多问题，但经过查阅资料并和学姐交流，最终解决了这些问题，以实验的方式验证课本上的理论知识，学习也变得更有意义。

－ 14 －