TCPIP协议原理与应用_第三版_Chapter04
Chapter 4 Solutions Answers to Review Questions
1.False
2. c
3.b, c ,d, e
4.True
5. a
6.a, c, d
7.True
8. b
9. a
10. d
11. c
12. a
13. b
14. b
15. d
16. b
17. d
18. c
19. c
20.b, c
21. d
22.False
23. c
24.a, d
25.b, c
Hands-on Projects Discussion
Project 4-1
In this project, students examine the ping command’s parameter list when they follow the step to type ping and press Enter. If the students have questions about the parameters listed, refer them to Appendix C where the parameters and their uses are listed. Students also learn how to open a window to provoke TCP/IP traffic that they capture in another window (the one running Ethereal). This is a common routine that networking professionals
follow when working with a protocol analyzer.
This lab illustrates one of the best ways to learn about protocols and traffic patterns. By launching the analyzer and then performing a task, the students create a record of the packets sent/received during the procedure. Reviewing the trace buffer reveals the underlying communication processes that support the procedure. These steps can be used to analyze all types of communication, including, but not limited to, file transfer, Web browsing, and login and logout procedures.
Project 4-2
In this project, the students build an address filter. Although this project requires the students to build an IP address filter, Ethereal supports the creation of physical (data link), IPv6, AppleTalk, and IPX filters, among many other kinds.
Upon review of this project, consider giving a short tour of the Ethereal filter string options and syntax. Explain to students that they may want to build and keep a master set of filters
that is configured to capture the traffic from key devices. For example, in a large company, a network analyst should always have a pre-built set of filters for the primary servers, routers, an d CEO’s computer. Likewise, they should get familiar with the Ethereal Filter reference that’s included as part of the program’s Help files.
Project 4-3
This is an interesting project because it requires that the students think about and add up the overhead used in each packet. The following answers are based on the results seen on an Ethernet network.
在tcpip参考模型中tcp协议工作在
1.Write your network’s maximum packet size (including headers). For example, Ethernet networks support
1,518 bytes:
1,518 bytes
2.Write the overhead of the Data Link layer header and trailer:
18 bytes (six-byte Source Address field, six-byte Destination Address field, two-byte Type field,
two-byte FCS field)
3.Write the overhead of the IP header:
20 bytes—options are not used on ICMP packets
4.Write the overhead of an ICMP header in an Echo Request packet:
Eight bytes (one-byte Type field, one-byte Code field, two-byte Checksum field, two-byte
Identifier field, two-byte Sequence field)
5.Subtract the values written for Steps 2, 3, and 4 from Step 1. Enter your result:
1518 - 18-– 20-– 8 = 1,472 bytes
In Step 7, the command would be ping -f -l 1472 ip_address, where 1472 is the MTU they a
re testing, and
ip_address is the device they are pinging.
In Step 8, the command would be ping -f -l 1474 ip_address, where 1474 is the MTU they are testing. They should see a message indicating that the Packet needs to be fragmented, but the DF (don’t fragment bit) was set. If the students want to capture a fragmented set, have them launch Ethereal (filtering on their own traffic) and enter the command used in Step 8, without the -f parameter.
Project 4-4
In this project, the students must open the ping.pkt trace file, and examine and compare the contents of the two packets. This project allows the students to practice looking at packet structures, locating fields, and identifying the function of the ICMP Checksum field. The following answer the project questions:
3a. What is the ICMP Identifier number in Packet #1?
0x0200
3b. What is the ICMP Sequence Number in Packet #1?
0x1100
3c. What is the ICMP Checksum value of Packet #1?
0x3A5C
4a. What is the ICMP Identifier number in Packet #2?
0x0200
4b. What is the ICMP Sequence Number in Packet #3?
0x1100
4c. What is the ICMP Checksum value of Packet #4?
0x425C
5. The ICMP Checksum value is different in each packet because the ICMP Checksum field is based on a checksum calculation of the entire ICMP header, including the Type and Code fields. The Type field is different in each packet. The Type field value in Packet #1 is eight. The Type field value in Packet #1 is zero.
Project 4-5
In this project, students must open the icmplab.pkt trace file and examine the ICMP reply to answer the following questions:
3a. What type of ICMP packet was sent?
The ICMP header of Packet #2 indicates that this is a Destination Unreachable ICMP message.

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