Instructor’s Manual Materials to Accompany
COMPUTER SECURITY FUNDAMENTALS
CHAPTER 2
NETWORKS AND THE INTERNET
CHAPTER 2 OBJECTIVES
When students finish reading this chapter, they will be able to:
• Describe the OSI model of network communication.
• Explain the use of MAC addresses.
• Identify each of the major protocols used in network communication (for example, FTP and Telnet) and
what use you can make of each.
• Understand the various connection methods and speeds used on networks.
• Compare and contrast a hub and switch.
• Identify what a router is and its use.
• Understand how data transmits over a network.
• Explain how the Internet works and the use of IP addresses and URLs.
• Use network utilities such as ping, IPConfig, and tracert.
• Explain the use of firewalls and proxy servers.
CHAPTER OVERVIEW
This chapter is a high-level summary on networking; however, you should receive a basic understanding of the
structure of networks, how they work, and knowledge of network utilities and devices. Protocols and devices are
described using the OSI model layers. You should also have an understanding of addressing and the Internet as a
network. This material will be critical in later chapters.
The major sections in this chapter are
1. The OSI Model. This is a learning tool to break up protocols into understandable layers.
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2. Networking Basics. Covers URLs, MAC, and IP addresses; protocols; cables; and devices and how they fit
in the OSI model.
3. Basic Network Utilities. The basic command-line networking utilities are presented: ipconfig, ping, and
tracert.
4. Other Network Devices. Firewalls and proxy servers are reviewed in more detail.
CHAPTER OUTLINE
I. Chapter 2 Objectives
II. Introduction
III. Network Basics
The Physical Connection: Local Networks
2. The Hub
Repeater
4. The Router
Faster Connections Speeds
Data Transmission
1. Protocols
2. Ports
IV. How the Internet Works
IP addresses
2. Subnetting and CIDR
4. IPv6
5.Uniform Resource Locators
History of the Internet
V. Basic Network Utilities
IPConfig
Ping
Tracert
VI. Other Network Devices
VII. Advanced Network Communications Topics
The OSI Model
Media Access Control (MAC) addresses
VII. Summary
IX. Test Your Skills
X. Exercises
XI. Projects
KEY TERMS
backbones The central Internet connections to which Internet Service Providers must ultimately con
nect.
binary numbers Numbers using the base 2. Ultimately, all data on a computer is stored in a base 2 format.
datagram A packet sent using the TCP protocol.
DNS servers/Domain Name Server A server that provides DNS Service.
Domain Name Service (DNS) A protocol that translates names, such as www.prenticehall.com, into an IP
address.
firewall A device or software that provides a barrier between your machine or network and the rest of the world.
hub A device for connecting computers.
Internet Protocol Security (IPSec) A protocol critical for securing virtual private networks.
Internet Service Provider (ISP) A company that provides Internet access for clients.
IP address A numerical designation for a computer consisting of four 1-byte binary numbers.
IPConfig A utility that provides extensive information about a computer’s network connection.
MAC addresses A unique hexadecimal number used to identify a network interface card.
Network Access Points (NAP) Places where you can connect to a network. This often used to refer to wireless
network connectivity points.
packet A binary piece of data prepared for transmission over a network.
ping To send a single ICMP packet to a destination, usually to confirm that the destination can be reached.
port A numerical designation for a connection point on a computer. There are well-defined ports for specific
protocols such as FTP port 21, HTTP port 80, and so forth.
protocols Agreed-upon methods of communication in networking that refer to ways to perform certain types of
communication, such as hypertext transfer protocol for web pages.
proxy server A machine or software that hides all internal network IP addresses from the outside world. It
provides a point of contact between a private network and the Internet.
router A device that separates networks.
server errors Errors that occur on the server rather than the client.
subnet A subsection of a network.
subnet mask A mask used to determine what subnet an IP address belongs to.
Transmission Control Protocol (TCP) A protocol used to send data over the Internet; part of the TCP/IP suite of
protocols.
User Datagram Protocol (UDP) A protocol similar to TCP except that transmissions are merely sent without any
attempt to confirm their arrival at the destination.
zone transfers DNS servers must update their list of what IP addresses go with what URL (Uniform Resource
Locator). They periodically perform zone transfers to synchronize those lists.
TEACHING NOTES
II. Network Basics
The Physical Connection: Local Networks
Teaching Tips: See whether you can bring in a cable, hub, switch, or router. Show
students how easy it is to hook up PCs to these devices. Demonstrate that it is difficult to tell the
difference between the three different devices on the outside. Explain that a hub broadcasts all the
network traffic to all ports. Ask students this question: “If someone were transmitting an ID and
password, how many PCs could hear it?”
The Physical Connection: Internet
Teaching Tips: See whether you can get local prices for T1, T3, and ISDN service.
Compare this to students’ cable and DSL speeds and services.
Teaching Tips: Datagrams are like telegrams. They not only contain data, but also
they need to have addressing and control information, such as who gets the telegram and “stop” after each
sentence.
Teaching Tips: Explain that TCP and IP are only two layers of the OSI model.
However, TCP/IP is actually a collection of protocols, two of which are TCP and IP. IP is the network
layer and is responsible for IP addresses and moving the packet to the correct computer. TCP and UDP sit
on top of IP. TCP can guarantee delivery at a cost of overhead. UDP is fast and efficient, but if a packet is
lost, there is no way to retrieve it. ICMP is the traffic cop, making sure that the data flow is OK.
Teaching Tips: Point out the difference between a physical layer port (RJ 45 on a
hub) and an application layer port used to connect applications over the Internet (port 23 telnet).
Application port numbers become important when there is a need to block some applications from
communicating.
Teaching Tips: The dotted decimal format of an IP address is just shorthand for
humans. Computers use the 32-binary IP address number just like the phone number of a computer with
only two buttons on the phone (1 and 0). The only thing a subnet mask does is to let the computer know
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LAN. This means that to communicate on the network a computer must have at least an IP address, the
subnet mask, and the default gateway. This display when you use ipconfig.
Teaching Tips: Explain that the data link, network, and application layers have
different addressing (MAC, IP, and URL). As the computer goes through the layers, the URL becomes an
IP address, which needs to end up with a MAC address using DNS and ARP.
V. Basic Network Utilities
Teaching Tips: Demonstrate these utilities in class. IPConfig tells you whether your
computer is configured correctly (using the DHCP services). Ping is a great way to tell whether you are
actually connected to a computer. Tracert helps to track where there may be a bottleneck or breakdown in
the network. Beware that Tracert and Ping traffic may be blocked at corporate firewalls.
Demonstrate Ping of 127.0.0.1 as a way to test whether TCP/IP is running on your
local computer.
VI. Other Network Devices
Teaching Tips: Firewalls can be complex devices. Some can filter only by protocol,
IP addresses, and port numbers. Others can detect potential attacks at the application level and block
them.
VII. The OSI Model
Teaching Tips: Of importance here is that the OSI is a tool to break up network
protocols into easy layers. This model helps to show what devices and protocols do in each layer. Not all
protocol stacks match exactly with the OSI model, but it helps as a teaching tool. You can use the
example of a normal conversation, using sound as the physical layer, and moving up to ideas in the
application layer. To convey an idea from one person to another, you need to go through all the layers
down to the sounds. The receiver then needs to take the sounds up the layers to an idea.
PROJECTS/EXERCISES
I. Discussion Questions
A. Discussion Question 1
Should all hubs be replaced with switches?
Answer: Students’ answers may vary. There should be discussion of cost versus security; a
hub is inexpensive but broadcasts all network traffic to all ports.
B. Discussion Question 2
If you were building your home, what cables would you install?
Answer: Students’ answers may vary. The issues are cost, transmission speed, and security.
See whether any students come up with wireless for an answer.
II. Web Projects
A. Web Project 1
Google your state’s building code to find out what cat type of cable is to be used
in new installations.
B. Web Project 2
Go to http://www.faqs.org/docs/linux_network/x-087-2-iface.ifconfig.html to
find out what the “if” in “ifconfig” stand for. How is it different from ipconfig? Where is
it used?
C. Web Project 3
Get a list of port number assignments from
http://www.iana.org/assignments/port-numbers. Find what used port 666. Would this be a
port that you may want to block?
D. Web Project 4
We keep hearing how IPv6 can save the Internet from the shortcomings of IPv4.
Google “IPv5.” What happened to this version of IP? A good place to start is
http://www.oreillynet.com/pub/wlg/3316.
WEB RESOURCES
Using web resources, look up the DNS protocol. You may find the following Web sites to be of help:
• http://www.freesoft.org/CIE/Topics/75.htm Freesoft.org, an Internet Encyclopedia; Domain Name
Service DNS topic
CHAPTER REVIEW/ANSWERS TO TEST YOUR SKILLS
Multiple Choice
1. The TCP protocol operates at what layer of the OSI model?
2. The layer of the OSI model that is divided into two sublayers is the
3. A unique hexadecimal number that identifies your network card is called a
4. What is a NIC?
5. A protocol that translates web addresses into IP addresses is called
6. The connector used with network cables is called
7. What type of cable do most networks use?
8. The cable used in networks is also referred to as
9. The simplest device for connecting computers is called a(n)
10. A device used to connect two or more networks together is a
11. A T1 line sends data at what speed?
12. How big is a TCP packet header?
13. What protocol is used to send e-mail, and on what port does it work?
14. What protocol is used for remotely logging on to a computer?
15. What protocol is used for web pages, and what port does it work on?
16. The point where the backbones of the Internet connect is called
17. The IP address of 193.44.34.12 would be in what class?
18. The IP address of 127.0.0.1 always refers to your
19. Internet addresses in the form of www.chuckeasttom.com are called
20. The utility that gives you information about your machine’s network configuration is
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Exercises
EXERCISE 2.1: USING IPCONFIG AND EXERCISE 2.2: USING TRACERT
Exercises 2.1 and 2.2 are simply procedural. Note if the students effectively use the utility; if so, then they have
EXERCISE 2.3: NSLOOKUP
EXERCISE 2.4: MORE ABOUT IPCONFIG AND EXERCISE 2.5: MORE ABOUT PING
Projects
PROJECT 2.1: LEARNING ABOUT DNS
The key to this project on DNS is for the student to learn more than simply what DNS does. The successful
PROJECT 2.2: LEARNING ABOUT YOUR SYSTEM
PROJECT 2.3: LEARNING ABOUT NETSTAT
This project asks the students to interpret the information they get from Netstat. Simply reporting on what the
Case Study
Although students have just been introduced to many topics in the first two chapters, this case study is designed to
get them thinking about how all this must come together for a successful and secure network. Answers should