Los ambientes para la innovación

■ When creating an Internet access strategy for a network, the first step is estimating how much Internet bandwidth the network needs. The Internet bandwidth needed by a network is based on the number of users and the types of applica­ tions they run.

■ WAN technologies such as dial-up modems, ISDN, CATV, DSL, leased lines, and frame relay provide varying amounts of bandwidth and operational characteristics, which you must evaluate before selecting one for an Internet connection.

■ ISPs can provide a variety of services to business clients in addition to providing simple Internet access. Part of the Internet access strategy is determining which ser­ vices you should implement in-house and which you should obtain from the ISP.

■ An Internet connection is a gateway that can work in both directions, enabling Internet users to access your private network as well as allowing your users Inter- net access. Security problems can also originate on the private network, from users who monopolize or abuse the Internet connection.

■ Most NAT implementations today use masquerading, a technique that maps unreg­ istered IP addresses to a single registered IP address combined with a port number.

■ Proxy server products have evolved to now include an array of firewall and access control features that provide comprehensive Internet security for a private network.

■ The first step in troubleshooting an Internet connectivity problem is to isolate its location. Reproducing the fault on other computers can tell you whether the prob­ lem is in the computer itself or in a component that affects other users as well.

■ To determine if an Internet connection problem is caused by a name resolution failure, which could be the result of an incorrect DNS server address or a malfunc­ tioning DNS server, try connecting to the Internet using an IP address instead of a DNS name.

■ NAT routers and proxy servers have network interfaces just like client computers, and they must have correct TCP/IP client configuration parameters. The configu­ ration of the NAT and proxy server functions must also be correct.

■ If no other components are at fault, the Internet connection problem might be caused by the Internet access router or the WAN connection to the ISP. The prob­ lem might also be caused by a service provider’s equipment, or even be in the Internet itself.

Exam Highlights

Before taking the exam, review the key points and terms that are presented below to help you identify topics you need to review. Return to the lessons for additional prac­ tice, and review the “Further Reading” sections in Part 2 for pointers to more informa­ tion about topics covering the exam objectives.

Key Points

■ The initial steps of Internet connectivity planning are to determine how much bandwidth the network needs and what WAN technology you should use to sup- ply that bandwidth.

■ To connect your network to the Internet using the WAN technology you’ve cho­ sen, you must decide what type of router to use at your site, what ISP you want to use, and what services you want the ISP to provide.

■ To provide users with Internet access safely, you should secure your network by using unregistered IP addresses and a NAT router or proxy server.

■ The first steps in troubleshooting Internet connectivity problems are to determine the scope of the problem and then isolate its location.

■ Internet connectivity problems are frequently caused by TCP/IP configuration errors, NAT router proxy server configuration errors, or malfunctioning WAN connections.

Key Terms

Network address translation (NAT) A router function that provides client comput­ ers with Internet access by substituting the router’s registered IP address for the clients’ unregistered addresses in individual data packets.

Stateful packet inspection An optional NAT feature that enables the router to inspect the contents of data packets for potentially damaging code.

Proxy server An application layer software product that functions as an intermedi­ ary between unregistered client computers and the Internet. In addition to provid­ ing Internet access, proxy servers can restrict Internet access, log Internet activity, and cache Internet data.

Questions and Answers

Page Lesson 1 Practice

3-13

Using the information provided in this lesson, place the following Internet connection technologies in order from lowest to highest, based on the amount of bandwidth they provide.

1. T-3

2. CATV

3. ISDN Basic Rate Interface

4. ADSL

5. Dial-up modem

6. T-1

e, c, b, d, f, a

Page Lesson 1 Review

3-13

1. Which of the following servers does not require a computer with a registered IP address?

a. Internet Web servers

b. Internet e-mail servers

c. DNS servers used for Internet domain hosting

d. DNS servers used for Internet name resolution d

2. Which of the following WAN technologies are asymmetrical? (Choose all answers that are correct.)

a. CATV

b. ISDN

c. ADSL

d. T-1 a and c

3. Which of the following Internet connection types enables you to save money when the network is not using any Internet bandwidth?

a. ISDN

b. DSL

c. Fractional T-1

d. Frame relay a and d

Page Lesson 2 Review

1. Which of the following components must you have for your network to run its own Internet e-mail server? (Choose all answers that are correct.)

a. A DNS server to host the domain

b. A registered IP address

c. A Web-based administration interface

d. A registered domain name a, b, and d

2. Internet access routers marketed as all-in-one devices typically include which additional services?

DHCP and NAT

3. List three advantages of using a larger, high-level ISP compared to a smaller one.