CCENT/CCNA ICND1 Official Exam Certification Guide - Chapter 12 pps

Part III: IP Routing Chapter 12 IP Addressing and Subnetting Chapter 13 Operating Cisco Routers Chapter 14 Routing Protocol Concepts and Configuration Chapter 15 Troubleshooting IP Routing 1828xbook.fm Page 329 Thursday, July 26, 2007 3:10 PM This chapter covers the following subjects: Exam Preparation Tools for Subnetting: This section lists the various tools that can help you practice your subnetting skills. IP Addressing and Routing: This section moves beyond the basic concepts in Chapter 5, “Fundamentals of IP Addressing and Routing,” introducing the purpose and meaning of the subnet mask. Math Operations Used When Subnetting: This section explains how to convert between IP address and subnet mask formats. Analyzing and Choosing Subnet Masks: This section explains the meaning behind subnet masks, how to choose a subnet mask to meet stated design goals, and how to interpret a mask chosen by someone else. Analyzing Existing Subnets: This section shows how to determine an IP address’s resident subnet, broadcast address, and range of addresses in the subnet. Design: Choosing the Subnets of a Classful Network: This section explains how to find all subnets of a single classful network. 1828xbook.fm Page 330 Thursday, July 26, 2007 3:10 PM C H A P T E R 12 IP Addressing and Subnetting The concepts and application of IP addressing and subnetting may well be the most important topics to understand both for being a well-prepared network engineer and for being ready to do well on the ICND1, ICND2, and CCNA exams. To design a new network, engineers must be able to begin with some IP address range and break it into subdivisions called subnets, choosing the right size of each subnet to meet design requirements. Engineers need to understand subnet masks, and how to pick the right masks to implement the designs that were earlier drawn on paper. Even more often, engineers need to understand, operate, and troubleshoot pre-existing networks, tasks that require mastery of addressing and subnetting concepts and the ability to apply those concepts from a different perspective than when designing the network. This chapter begins Part III of the book, which is focused on the role of routers in an internetwork. As introduced in Chapter 5, the network layer defines and uses addressing, routing, and routing protocols to achieve its main goals. After this chapter goes into depth on addressing, the rest of the chapters in Part III focus on how to implement IP addresses, routing, and routing protocols inside Cisco routers. All the topics in this chapter have a common goal, which is to help you understand IP addressing and subnetting. To prepare you for both real jobs and the exams, this chapter goes far beyond the concepts as covered on the exam, preparing you to apply these concepts when designing a network and when you operate and troubleshoot a network. Additionally, this chapter creates a structure from which you can repeatedly practice the math processes used to get the answers to subnetting questions. “Do I Know This Already?” Quiz The “Do I Know This Already?” quiz allows you to assess if you should read the entire chapter. If you miss no more than one of these 14 self-assessment questions, you might want to move ahead to the “Exam Preparation Tasks” section. Table 12-1 lists the major headings in this chapter and the “Do I Know This Already?” quiz questions covering the material in those headings so you can assess your knowledge of these specific areas. The answers to the “Do I Know This Already?” quiz appear in Appendix A. 1828xbook.fm Page 331 Thursday, July 26, 2007 3:10 PM 332 Chapter 12: IP Addressing and Subnetting 1. Which of the following are private IP networks? a. 172.31.0.0 b. 172.32.0.0 c. 192.168.255.0 d. 192.1.168.0 e. 11.0.0.0 2. Which of the following is the result of a Boolean AND between IP address 150.150.4.100 and mask 255.255.192.0? a. 1001 0110 1001 0110 0000 0100 0110 0100 b. 1001 0110 1001 0110 0000 0000 0000 0000 c. 1001 0110 1001 0110 0000 0100 0000 0000 d. 1001 0110 0000 0000 0000 0000 0000 0000 3. Which of the following shows the equivalent of subnet mask 255.255.248.0, but in prefix notation? a. /248 b. /24 c. /28 d. /21 e. /20 f. /23 Table 12-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping Foundation Topics Section Questions Exam Preparation Tools for Subnetting None IP Addressing and Routing 1 Math Operations Used When Subnetting 2, 3 Analyzing and Choosing Subnet Masks 4–8 Analyzing Existing Subnets 9–12 Design: Choosing the Subnets of a Classful Network 13, 14 1828xbook.fm Page 332 Thursday, July 26, 2007 3:10 PM “Do I Know This Already?” Quiz 333 4. If mask 255.255.255.128 were used with a Class B network, how many subnets could exist, with how many hosts per subnet, respectively? a. 256 and 256 b. 254 and 254 c. 62 and 1022 d. 1022 and 62 e. 512 and 126 f. 126 and 510 5. A Class B network needs to be subnetted such that it supports 100 subnets and 100 hosts/subnet. For this design, if multiple masks meet those design requirements, the engineer should choose the mask that maximizes the number of hosts per subnet. Which of the following masks meets the design criteria? a. 255.255.255.0 b. /23 c. /26 d. 255.255.252.0 6. If mask 255.255.255.240 were used with a Class C network, how many subnets could exist, with how many hosts per subnet, respectively? a. 16 and 16 b. 14 and 14 c. 16 and 14 d. 8 and 32 e. 32 and 8 f. 6 and 30 7. Which of the following subnet masks lets a Class B network have up to 150 hosts per subnet, and supports 164 subnets? a. 255.0.0.0 b. 255.255.0.0 c. 255.255.255.0 d. 255.255.192.0 e. 255.255.240.0 f. 255.255.252.0 1828xbook.fm Page 333 Thursday, July 26, 2007 3:10 PM 334 Chapter 12: IP Addressing and Subnetting 8. Which of the following subnet masks let a Class A network have up to 150 hosts per subnet and supports 164 subnets? a. 255.0.0.0 b. 255.255.0.0 c. 255.255.255.0 d. 255.255.192.0 e. 255.255.252.0 f. 255.255.255.192 9. Which of the following IP addresses are not in the same subnet as 190.4.80.80, mask 255.255.255.0? a. 190.4.80.1 b. 190.4.80.50 c. 190.4.80.100 d. 190.4.80.200 e. 190.4.90.1 f. 10.1.1.1 10. Which of the following IP addresses is not in the same subnet as 190.4.80.80, mask 255.255.240.0? a. 190.4.80.1 b. 190.4.80.50 c. 190.4.80.100 d. 190.4.80.200 e. 190.4.90.1 f. 10.1.1.1 11. Which of the following IP addresses are not in the same subnet as 190.4.80.80/25? a. 190.4.80.1 b. 190.4.80.50 c. 190.4.80.100 d. 190.4.80.200 e. 190.4.90.1 f. 10.1.1.1 1828xbook.fm Page 334 Thursday, July 26, 2007 3:10 PM “Do I Know This Already?” Quiz 335 12. Each of the following answers lists a dotted decimal number and a subnet mask. The dotted decimal number might be a valid IP address that can be used by a host or it might be a subnet number or broadcast address. Which of the answers show an address that can be used by a host? a. 10.0.0.0, 255.0.0.0 b. 192.168.5.160, 255.255.255.192 c. 172.27.27.27, 255.255.255.252 d. 172.20.49.0, 255.255.254.0 13. Which of the following are valid subnet numbers in network 180.1.0.0 when using mask 255.255.248.0? a. 180.1.2.0 b. 180.1.4.0 c. 180.1.8.0 d. 180.1.16.0 e. 180.1.32.0 f. 180.1.40.0 14. Which of the following are not valid subnet numbers in network 180.1.0.0 when using mask 255.255.255.0? a. 180.2.2.0 b. 180.1.4.0 c. 180.1.8.0 d. 180.1.16.0 e. 180.1.32.0 f. 180.1.40.0 1828xbook.fm Page 335 Thursday, July 26, 2007 3:10 PM 336 Chapter 12: IP Addressing and Subnetting Foundation Topics This chapter is fundamentally different from the other chapters in this book. Like the other chapters, this chapter explains a related set of concepts—in this case, the concepts, thought processes, and math used to attack IP addressing and subnetting questions on the CCNA exams. However, more so than for any other chapter in this book, you must practice the concepts and math in this chapter before you take the exam(s). It is very much like math classes in school—if you do not do the homework, you probably will not do as well on the test. This chapter begins with a few comments about how to prepare for subnetting questions on the exam. Then the chapter spends a few pages reviewing what has been covered already in regard to IP addressing and routing, two topics that are tightly linked. The rest of the major sections of the chapter tackle a particular type of subnetting question in depth, with each section ending with a list of suggested steps to take to practice your subnetting skills. Exam Preparation Tools for Subnetting To help you prepare for the exam, this chapter explains the subnetting concepts and shows multiple examples. Each section also lists the specific steps required to solve a particular type of problem. Often, two sets of steps are provided, one that uses binary math, and another that uses only decimal math. More so than for any other single chapter in this book, you should also practice and review the topics in this chapter until you have mastered the concepts. To that end, this book includes several tools, some of which are located on the CD-ROM that comes with this book, in addition to this chapter: ■ Appendix D, “Subnetting Practice”: This large appendix lists numerous practice problems, with solutions that show how to use the processes explained in this chapter. ■ Appendix E, “Subnetting Reference Pages”: This short appendix includes a few handy references, including a 1-page summary of each of the subnetting processes listed in this chapter. ■ Subnetting videos (DVD): Several of the most important subnetting processes described in this chapter are explained in videos on the DVD in the back of this book. The goal of these videos is to ensure that you understand these key processes completely, and hopefully move you quickly to the point of mastering the process. ■ Cisco Binary Game at the Cisco CCNA Prep Center: If you want to use the processes that use binary math, you can use the Cisco Binary Game to practice your 1828xbook.fm Page 336 Thursday, July 26, 2007 3:10 PM Exam Preparation Tools for Subnetting 337 binary-to-decimal and decimal-to-binary conversion accuracy and speed. The CCNA Prep Center is at http://www.cisco.com/go/prepcenter. The binary game is also included on the CD in the back of the book. ■ Subnetting Game at the Cisco CCNA Prep Center: As of the time of writing this chapter, the CCNA Prep Center had a Beta version of the Subnetting Game available. The game requires that you choose a mask, pick subnets, calculate the subnet number and broadcast address of the subnets, and assign IP addresses in the subnets. ■ Subnetting calculators: You can make up your own practice problems, and use a subnetting calculator to find the answers to check your work. This allows you to have unlimited amounts of practice to get better and get faster. The CCNA Prep Center also has the Cisco Subnet Calculator for free download. ■ Glossary: The topics of IP addressing and subnetting use a wide variety of terminology. The glossary in the back of this book includes the subnetting terms used in this book. Suggested Subnetting Preparation Plan Over the years, some readers have asked for a suggested subnetting study plan. At the same time, the CCNA exam questions have been getting more difficult. To help you better prepare, the following list outlines a suggested study plan: Step 1 If you have not done so already, load the CD-ROM and get familiar with its user interface, install the exam engine software, and verify that you can find the tools listed in the preceding list. You may want to go ahead and print Appendix E, and if you expect you will want to use a printed version of Appendix D, print that as well (be warned, Appendix D is almost 100 pages in length). Step 2 Keep reading this chapter through the end of the second major section, “IP Addressing and Routing.” Step 3 For each subsequent major section, read the section and then follow the instructions in the subsection “Practice Suggestions.” This short part of each major section points you to the items that would be of the most help to stop and practice at that point. These suggestions include the use of the tools listed earlier. The following major sections include a “Practice Suggestions” subsection: • Math Operations Used When Subnetting • Analyzing and Choosing Subnet Masks • Analyzing Existing Subnets • Design: Choosing the Subnets of a Classful Network 1828xbook.fm Page 337 Thursday, July 26, 2007 3:10 PM 338 Chapter 12: IP Addressing and Subnetting Step 4 When finished with the chapter, if you feel the need for more practice, make up your own practice problems, and check your answers using a subnet calculator (more information is provided after this list). I recommend the Cisco Subnet Calculator because its user interface displays the information in a convenient format for doing extra questions. Step 5 At any point in your study, feel free to visit the CCNA Prep Center (http://www.cisco.com/go/prepcenter) to use both the Cisco Binary Game and the Subnetting Game. Both help you build skills for doing subnetting problems. (The CCNA Prep Center requires you to log in with a Cisco.com User ID; if you do not have one, the preceding URL has a link to Cisco.com registration.) Once in the CCNA Prep Center, you can find the games under the Additional Information tab. You can certainly deviate from this plan to suit your personal preferences, but at the end of this process, you should be able to confidently answer straightforward subnetting questions, such as those in Appendix D. In fact, you should be able to answer in 10–12 seconds a straightforward question such as, “In what subnet does IP address 10.143.254.17, with mask 255.255.224.0, reside?” That is a subjective time period, based on my experience teaching classes, but the point is that you need to understand it all, and practice to the point of being pretty fast. However, perfecting your subnetting math skills is not enough. The exams ask questions that require you to prove you have the skills to attack real-life problems, problems such as how to design an IP network by subnetting a classful network, how to determine all the subnets of a classful network, and how to pick subnets to use in an internetwork design. The wording of the exam problems, in some cases, is similar to that of the math word problems back in school—many people have trouble translating the written words into a math problem that can be worked. Likewise, the exam questions may well present a scenario, and then leave it to you to figure out what subnetting math is required to find the answer. To prepare for these skills-based questions, Chapter 15, “Troubleshooting IP Routing,” covers a wide variety of topics that help you analyze a network to solve subnetting-related problems. These extra tips help you sift through the wording in problems, and tell you how to approach the problems, so that you can then find the answers. So, in addition to this chapter, read through Chapter 15 as well, which includes coverage of tips for troubleshooting IP addressing problems. More Practice Using a Subnet Calculator If you want even more practice, you can essentially get unlimited practice using a subnet calculator. For the purpose of CCNA study, I particularly like the Cisco Subnet Calculator, which can be downloaded from the Cisco CCNA Prep Center. You can then make up your 1828xbook.fm Page 338 Thursday, July 26, 2007 3:10 PM [...]... subnet has a 24-bit prefix” instead of saying something like “That subnet uses a mask of two-fifty-five dot two-fifty-five dot two-fifty-five dot two-fifty-five.” As you can tell, the prefix notation alternative—simply saying something like “slash twenty-four”—is much easier Binary Process to Convert Between Dotted Decimal and Prefix Notation To be prepared for both real networking jobs and the exams, you should... broadcast address) and network 127 .0.0.0 (still available for use as the loopback address) are reserved 339 1828xbook.fm Page 340 Thursday, July 26, 2007 3:10 PM 340 Chapter 12: IP Addressing and Subnetting Table 1 2-2 List of All Possible Valid Network Numbers Class A Class B Class C First Octet Range 1 to 126 128 to 191 192 to 223 Valid Network Numbers 1.0.0.0 to 126 .0.0.0 128 .0.0.0 to 191.255.0.0 192.0.0.0... Subnet Masks Table 1 2-1 0 shows an example, with the last three rows showing the analysis of the three parts of the IP address based on the three rules just listed (If you have forgotten the ranges of values in the first octet for addresses in Class A, B, and C networks, refer to Table 1 2-2 .) Table 1 2-1 0 First Example, with Rules for Learning the Network, Subnet, and Host Part Sizes Step Example Rules to... 2007 3:10 PM 364 Chapter 12: IP Addressing and Subnetting If you do not want to keep plugging values into the formulas based on 2x, you can instead memorize Table 1 2-1 4 Table 1 2-1 4 Maximum Number of Subnets/Hosts Number of Bits in the Host or Subnet Field Maximum Number of Hosts (2h – 2) Maximum Number of Subnets (2s ) 1 0 2 2 2 4 3 6 8 4 14 16 5 30 32 6 62 64 7 126 128 8 254 256 9 510 512 10 1022 1024... subnets 343 1828xbook.fm Page 344 Thursday, July 26, 2007 3:10 PM 344 Chapter 12: IP Addressing and Subnetting Figure 1 2-2 shows a reminder of the basics of how to subnet a classful network, using the same internetwork shown in Figure 5-6 in Chapter 5 This figure shows Class B network 150.150.0.0, with a need for six subnets Figure 1 2-2 Same Network Topology Using One IP Network with Six Subnets 150.150.1.0... want more information: ■ For a description of the conversion process, try http://doit.ort.org/course/inforep/135.htm ■ For another, try http://www.wikihow.com/Convert-from-Binary-to-Decimal and http://www.wikihow.com/Convert-from-Decimal-to-Binary ■ To practice the conversions, use the Cisco Binary Game at the CCNA Prep Center (http://www.cisco.com/go/prepcenter) Performing a Boolean AND Operation George... 350 Chapter 12: IP Addressing and Subnetting AND together two four-digit numbers, 0110 and 0011, you would perform an AND on the first digit of each number and write down the answer Then you would perform an AND operation on the second digit of each number, and so on, through the four digits Table 1 2-7 shows the general idea Table 1 2-7 Bitwise Boolean AND Between Two Four-Digit Numbers Four-Digit Binary... you need to understand this process In this chapter, you will also read about a process by which you can find the subnet number without using binary conversion or Boolean ANDs Table 1 2-8 shows an example of the derivation of a subnet number 1828xbook.fm Page 351 Thursday, July 26, 2007 3:10 PM Math Operations Used When Subnetting Table 1 2-8 Bitwise Boolean AND Example Decimal Binary Address 150.150.2.1... mask allows you to easily find the size of the network, subnet, and host parts of addresses in a particular subnetting scheme For example, consider the addresses and masks, including the binary versions of the masks, shown in Table 1 2-1 1 Table 1 2-1 1 Two Examples Using More-Challenging Masks Mask in Decimal Mask in Binary 130.4.102.1, mask 255.255.252.0 1111 1111 1111 1111 1111 1100 0000 0000 199.1.1.100,... listed, then the zero subnet and the other special subnet, the broadcast subnet, are both allowed For the exams, any time that the zero subnet or broadcast subnet may impact the answer to the question, use the information in Table 1 2-1 2 to help you decide whether to allow these two special subnets Table 1 2-1 2 When to Use Which Formula for the Number of Subnets Use the 2s – 2 formula, and avoid the zero and . 3:10 PM 336 Chapter 12: IP Addressing and Subnetting Foundation Topics This chapter is fundamentally different from the other chapters in this book. Like the other chapters, this chapter explains. read the entire chapter. If you miss no more than one of these 14 self-assessment questions, you might want to move ahead to the Exam Preparation Tasks” section. Table 1 2-1 lists the major. /24 c. /28 d. /21 e. /20 f. /23 Table 1 2-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping Foundation Topics Section Questions Exam Preparation Tools for Subnetting None IP