实验一 Ethernet and ARP一、实验目的1.加强对以太网帧格式的理解；2.理解ARP协议的工作原理。二、实验环境1.PC机一台；2.WireShark软件。三、实验内容1. Capturing and analyzing Ethernet frames2. The Address Resolution Protocol四、实验步骤及思考（一）Capturing and analyzing Ethernet framesHTTP GET Message(1)Based on the contents of the Ethernet frame containing the HTTP GET message1. What is the 48-bit Ethernet address of your computer?Answer：The 48-bit Ethernet address of my computer is:c8:0a:a9:db:9b:f3The Ethernet address of my computer2. What is the 48-bit destination address in the Ethernet frame? Is this the Ethernet address of gaia.cs.umass.edu? (Hint: the answer is no). What device has this as its Ethernet address?Note: this is an important question, and one that students sometimes get wrong. Re-read pages 468-469 in the text and make sure you understand the answer here.Answer：1)The 48-bit destination address in the Ethernet frame is:00:23:89:8d:50:71The destination address in the Ethernet frame2)This is not the Ethernet address of gaia.cs.umass.edu.3)It is the address of my Linksys router, whick is the link used to get off the subnet. 3.Give the hexadecimal value for the two-byte Frame type field. What do the bit(s) whose value is 1 mean within the flag field? Answer：1)The hexadecimal value for the two-byte Frame type field is:ox0800The hexadecimal value for the two-byte Frame type field2) The value is 1 within the flag field means the fragment has not been fragmented.Flag4.How many bytes from the very start of the Ethernet frame does the ASCII “G” in “GET” appear in the Ethernet frame?Answer：1)The ASCII “G” appears 54 bytes from the very start of the Ethernet frame.2)Calculation process as follows:There are 14 bytes of Ethernet frame,20 bytes of IP header and 20 bytes of TCP header before HTTP data is encountered.5. What is the hexadecimal value of the CRC field in this Ethernet frame? Answer：1)There is no CRC field.2)Because the CRC calculated before the Wireshark packet sniffer start up.No CRC(2)Based on the contents of the Ethernet frame containing the first byte of the HTTP response message6. What is the value of the Ethernet source address? Is this the address of your computer, or of gaia.cs.umass.edu (Hint: the answer is no). What device has this as its Ethernet address?Answer：1)The value of the Ethernet source address is: 00:23:89:8d:50:71HTTP response message2)This is neither the address of your computer,northe address of gaia.cs.umass.edu.3)It is the address of my Linksys router,which is the link used to get onto my subnet.7. What is the destination address in the Ethernet frame? Is this the Ethernet address of your computer?Answer：1)The destination address in the Ethernet frame is:c8:0a:a9:db:9b:f32)It is the address of my computer. (The 48-bit Ethernet address of my computer is:c8:0a:a9:db:9b:f3)8. Give the hexadecimal value for the two-byte Frame type field. What do the bit(s) whose value is 1 mean within the flag field?Answer：1)The hexadecimal value for the two-byte Frame type field is: 0x0800.2)The value is 1 within the flag field means the fragment has not been fragmented.Flag field9. How many bytes from the very start of the Ethernet frame does the ASCII “O” in “OK” (i.e., the HTTP response code) appear in the Ethernet frame?Answer：1)The ASCII “O” appears 54 bytes from the very start of the Ethernet frame.2)Calculation process as follows:There are 14 bytes of Ethernet frame,20 bytes of IP header and 20 bytes of TCP header before HTTP data is encountered.10. What is the hexadecimal value of the CRC field in this Ethernet frame?Answer：1)There is no CRC field.2)The reason:Because the CRC calculated before the Wireshark packet sniffer start up.(二)The Address Resolution Protocol（1）ARP Caching11. Write down the contents of your computers ARP cache. What is the meaning of each column value?Answer： 1)The Internet Address column contains the IP address,.2)The Physical Address column contains the MAC address, and the type indicates the protocol type.3)Observing ARP in action12. What are the hexadecimal values for the source and destination addresses in the Ethernet frame containing the ARP request message?Answer：1)The hexadecimal values for the source addresses in the Ethernet frame containing the ARP request message is: 00:23:89:8d:50:712)The destination addresses in the Ethernet frame containing the ARP request message is: ff:ff:ff:ff:ff:ff13. Give the hexadecimal value for the two-byte Ethernet Frame type field. What do the bit(s) whose value is 1 mean within the flag field?Answer：The hexadecimal value for the two-byte Ethernet Frame type field is:0x0806.14. Download the ARP specification from ftp:/ftp.rfc-editor.org/innotes/std/std37.txt. A readable, detailed discussion of ARP is also at http:/www.erg.abdn.ac.uk/users/gorry/course/inet-pages/arp.html.a) How many byt