FitzGerald J., Dennis A., Durcikova A. Business Data Communications and Networking

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HANDS-ON ACTIVITY 8C 305

FIGURE 8.19 Viewing encrypted packets

306 CHAPTER 8 WIDE AREA NETWORKS

FIGURE 8.20 Packets that enter the VPN tunnel

HANDS-ON ACTIVITY 8C 307

change the size and shape of this window, but it

is not as ﬂexible as a usual window.

2. We will ﬁrst trace the route from your computers

to two other computers without using the VPN. So

make sure your VPN is not connected.

3. We’ll start by tracing the route from your computer

to a computer on the campus of the site you VPN

into. In my case, I VPN into my university, which

is Indiana University. I can choose to trace the

route to any computer on campus. I’ll choose our

main Web server (www.iu.edu). At the command

prompt, type tracert and the URL of a computer

on your campus.

4. The top half of Figure 8.21 shows the route from

my computer to www.iu.edu. There are 18 hops

and it takes about 35 ms. The ﬁrst hop does not

report information because this feature is turned

off in the router at my house for security reasons.

You can see that my ISP is Comcast (hop 6). If you

compare this to the tracert at the end of Chapter 5,

you’ll notice that my ISP changed (and thus the

route into the Internet changed) between the time I

wrote Chapter 5 and this chapter; Comcast bought

Insight in my town of Bloomington, Indiana.

5. Now trace the route from your computer to

another computer on the Internet. The bottom of

Figure 8.21 shows the route from my computer to

www.google.com. There are 17 hops, and it takes

about 35 ms. You’ll see that the routes to IU and

Google are the same until step 6, and then they

diverge.

6. Next we want to see what happens when you have

a VPN connection. Start your VPN software and

connect into the VPN gateway at your school.

7. Trace the route from your computer to the same

computer as in step 3. At the command prompt,

type tracert and the URL of a computer on your

campus.

8. The top half of Figure 8.22 shows the route from

my computer to www.iu.edu. There are two hops

and it takes about 35 ms. The VPN is in opera-

tion and is transparent to my networking software,

which thinks it is on the same subnet as the VPN

gateway. Therefore, it thinks there is just one hop

from my computer to the subnet’s gateway, the

VPN gateway. You’ll see that the time is still about

35 ms, so the packet is still traveling the s ame 18

hops to get there; it’s just that the tracert packet is

encapsulated and doesn’t see all the hops through

the VPN tunnel.

9. Now do a tracert to the same computer as you

did in step 5. The bottom of Figure 8.22 shows

the route from my computer to www.google.com.

There are nine hops and it takes about 43 ms. Of

course, the ﬁrst hop is really 17 hops and 35 ms;

this is again hidden from view. As we explained

in the text, when the VPN is connected, all pack-

ets go from your computer to the VPN gateway

on your campus before being routed to the ﬁnal

destination. You can see from this ﬁgure that this

adds additional hops and time to packets that are

not going to your campus, compared to not using

the VPN. You can also see that once the packets

leave the VPN gateway they are ordinary packets;

they are no longer encrypted and protected from

view.

The VPN provides security only to and from

the VPN gateway on your campus, not beyond

it. Therefore, you should use your VPN if you

have security concerns to and from campus (e.g.,

someone snifﬁng your packets). But if most of

your work is going to be off campus, then the

VPN increases the time it takes to send and

receive packets, and only provides security pro-

tection over the last section from your computer

to your school’s campus. Using the VPN may not

be worth the additional response time it imposes

on you.

Deliverables

1. What are the routes from your computer to your

campus Web server with and without the VPN?

2. What are the routes from your computer to

www.google.com with and without the VPN?

308 CHAPTER 8 WIDE AREA NETWORKS

FIGURE 8.21 TraceRt without a VPN

HANDS-ON ACTIVITY 8C 309

FIGURE 8.22 TraceRt with a VPN

CHAPTER9

THE INTERNET

The Three Faces of Networking

Fundamental Concepts Network Technologies

The Internet

Network Management

ecurit

Application layer

Network layer

Data Link layer

Physical layer

LAN

WLAN

Transport layer

Backbone

WAN

Internet

9.1 INTRODUCTION 311

THIS CHAPTER examines the Internet in more detail to explain

how it works and why it is a network of networks. The chapter also examines

Internet access technologies, such as DSL and cable modem, as well as the

possible future of the Internet

OBJECTIVES

▲

 Understand the overall design of the Internet

 Be familiar with DSL, cable modem, ﬁber to the home, and WiMax

 Be familiar with possible future directions of the Internet

CHAPTER OUTLINE

▲

9.1 INTRODUCTION

9.2 HOW THE INTERNET WORKS

9.2.1 Basic Architecture

9.2.2 Connecting to an ISP

9.2.3 The Internet Today

9.3 INTERNET ACCESS TECHNOLOGIES

9.3.1 Digital Subscriber Line (DSL)

9.3.2 Cable Modem

9.3.3 Fiber to the Home

9.3.4 WiMax

9.4 THE FUTURE OF THE INTERNET

9.4.1 Internet Governance

9.4.2 Building the Future

9.5 IMPLICATIONS FOR MANAGEMENT

9.1 INTRODUCTION

The Internet is the most used network in the world, but it is also one of the least under-

stood. There is no one network that is the Internet. Instead, the Internet is a network of

networks—a set of separate and distinct networks operated by various national and state

government agencies, nonproﬁt organizations, and for-proﬁt corporations. The Internet

exists only to the extent that these thousands of separate networks agree to use Internet

protocols and to exchange data packets among one another.

When you are on the Internet, your computer, (iPad, smart phone, etc.) is connected

to the network of an Internet Service Provider (ISP) that provides network services for

you. Messages ﬂow between your client device and the ISP’s network. Suppose you

request a Web page on CNN.com, a Web site that is outside of your ISP’s network.

Your HTTP request ﬂows from your device through your ISP’s network and through

other networks that link your ISP’s network to the network of the ISP that provides

Internet services for CNN. Each of these networks is separate and charges their own

customers for Internet access, but permit trafﬁc from other networks to ﬂow through

312 CHAPTER 9 THE INTERNET

You are here

FIGURE 9.1 The

internet is a lot like the

universe—many

independent systems

linked together

Source: Photo 14 at

http://grin.hq.nasa.gov/

BROWSE/gallaxies.html

them. In many ways, the Internet is like the universe (see Figure 9.1). Each of us works

in our own planet with its own rules (i.e., ISP) but each planet is interconnected with all

the others.

The Internet is simultaneously a strict, rigidly controlled club in which deviance

from the rules is not tolerated and a freewheeling, open marketplace of ideas. All networks

that connect to the Internet must rigidly conform to an unyielding set of standards for the

transport and network layers; without these standards, data communication would not be

possible. At the same time, content and new application protocols are developed freely

and without restriction, and quite literally anyone in the world is allowed to comment

on proposed changes.

In this chapter, we ﬁrst explain how the Internet really works and look inside one of

the busiest intersections on the Internet, the Chicago network access point, at which 100

separate Internet networks meet to exchange data. We then turn our attention to how you

as an individual can access the Internet and what the Internet may look like in the future.

9.2 HOW THE INTERNET WORKS

9.2.1 Basic Architecture

The Internet is hierarchical in structure. At the top are the very large national Internet

Service Providers (ISPs), such as AT&T and Sprint, that are responsible for large Internet

networks. These national ISPs, called tier 1 ISPs, connect together and exchange data

at network access points (NAPs) (Figure 9.2). For example, AT&T, Sprint, Verizon,

9.2 HOW THE INTERNET WORKS 313

Tier 1 ISP

Tier 3 ISP

Tier 2 ISP

Tier 2 ISPTier 2 ISP

Tier 2 ISP

Tier 1 ISP

NAP

MAE

FIGURE 9.2 Basic Internet architecture. ISP = Internet service provider;

MAE = metropolitan area exchange; NAP = network access point

Qwest, Level 3, and Global Crossing are all tier 1 ISPs that have a strong presence in

North America.

In the early 1990s, when the Internet was still primarily run by the U.S. National

Science Foundation (NSF), the NSF established four main NAPs in the United States to

connect the major tier 1 ISPs. When the NSF stopped funding the Internet, the companies

running these NAPs began charging the ISPs for connections, so today the NAPs in the

United States are all not-for-proﬁt organizations or commercial enterprises run by various

common carriers such as AT&T and Sprint. As the Internet has grown, so too has the

number of NAPs; today there are about a dozen NAPs in the United States with many

more spread around the world.

Network access points were originally designed to connect only large tier 1 ISPs.

These ISPs in turn provide services for their customers and also to regional ISPs (some-

times called tier 2 ISPs) such as Cogent Communications Comcast, or France Telcom.

These tier 2 ISPs rely on the tier 1 ISPs to transmit their messages to ISPs in other

countries. Tier 2 ISPs, in turn, provide services to their customers and to local ISPs

(sometimes called ISPs) who sell Internet access to individuals. As the number of ISPs

grew, a new form of NAP called a metropolitan area exchange (MAE) emerged. MAEs

are smaller versions of NAPs and typically link a set of regional ISPs whose networks

come together in major cities (Figure 9.2).

314 CHAPTER 9 THE INTERNET

Because most NAPs, MAEs, and ISPs now are run by commercial ﬁrms, many of

the early restrictions on who could connect to whom have been lifted. Most now openly

solicit business from all tiers of ISPs and even large organizations. Regional and local

ISPs often will have several connections into other ISPs to provide backup connections

in case one Internet connection fails. In this way, they are not dependent on just one

higher-level ISP.

In general, ISPs at the same level do not charge one another for transferring mes-

sages they exchange. That is, a national tier 1 ISP does not charge another national tier 1

ISP to transmit its messages. This is called peering. Figure 9.2 shows several examples

of peering. It is peering that makes the Internet work and has led to the belief that

the Internet is free. This is true to some extent, but higher-level ISPs normally charge

lower-level ISPs to transmit their data (e.g., a tier 1 will charge a tier 2 and a tier 2 will

charge a tier 3). And of course, any ISP will charge individuals like us for access!

In October 2005, an argument between two national ISPs shut down 45 million

Web sites for a week. The two ISPs had a peering agreement but one complained that

the other was sending it more trafﬁc than it should so it demanded payment and stopped

accepting trafﬁc, leaving large portions of the network isolated from the rest of the

Internet. The dispute was resolved, and they began accepting trafﬁc from each other and

the rest of the Internet again.

Peering has risen to a new level in recent years with the arrival of Internet

Exchange Points (IXPs). An IXP, which is often run by a not-for-proﬁt cooperative

organization, permits any ISP (or large organization) to connect to its network. Some

IXPs charge connection fees, others charge membership fees, and others don’t charge at

all. Once connected to the IXP, the ISP negotiates peering agreements with other ISPs

who are members of the IXP, and then begins exchanging Internet trafﬁc.

In Figure 9.2, each of the ISPs are autonomous systems, as deﬁned in Chapter 5.

Each ISP is responsible for running its own interior routing protocols and for exchang-

ing routing information via the Border Gateway Protocol (BGP) exterior routing pro-

tocol (see Chapter 5) at NAPs, MAEs, IXPs, and any other connection points between

individual ISPs.

9.2.2 Connecting to an ISP

Each of the ISPs is responsible for running its own network that forms part of the Internet.

ISPs make money by charging customers to connect to their part of the Internet. Local

ISPs charge individuals for broadband or dial-up access whereas national and regional

ISPs (and sometimes local ISPs) charge larger organizations for higher-speed access.

Each ISP has one or more points of presence (POP). A POP is simply the place at

which the ISP provides services to its customers. To connect into the Internet, a customer

must establish a circuit from his or her location into the ISP POP. For individuals, this is

often done using a DSL modem or cable modem (Figure 9.3). This connects to the DSL

multiplexer at the ISP and from there to a remote-access server (RAS), which checks

to make sure the user is a valid customer. Once logged in, the user can begin sending

TCP/IP packets from his or her computer to the POP. Figure 9.3 shows a POP using a

switched backbone with a layer-2 switch. The POP backbone can take many forms, as

we discussed in Chapter 7.