CCNA Exam Questions: Subnetting, VLSM, and IPv6

1. Quick Check Answer Key
2. Answers and Explanations
This chapter is from the book

This chapter is from the book 

1. C. 172.16.0-3.0/22 breaks down into the following binary equivalents:

 172.16.0.0 = 10101100.00010000.00000000.00000000 172.16.1.0 = 10101100.00010000.00000001.00000000 172.16.2.0 = 10101100.00010000.00000010.00000000 172.16.3.0 = 10101100.00010000.00000011.00000000

Based on these binary values, you can see that the first 22 bits on each one of these IP addresses are the same. This makes the accurate summary address 172.16.0.0/22. All other answers are not valid.

2. D. To find the valid number of hosts on a subnet, use the formula (2x) – 2, where "x" is the number of host bits in the subnet mask. A /21 (255.255.248.0) subnet mask has 11 host bits. (211) – 2 = 2046. All other answers are not valid.
3. C, F. These styles of VLSM are common on the ICND2/CCNA exam. It's usually best to reverse-engineer the given subnets to see what ranges are in use and then compare the answers to fill in what's left over. In this case, the given ranges are:

• 192.168.1.32-63/27 (Behind the Oracle router)
• 192.168.1.64-95/27 (Behind the Morpheus router)
• 192.168.1.96-111/28 (Behind the Trinity router)
• 192.168.1.4-7/30 (Neo-Oracle WAN link)
• 192.168.1.8-11/30 (Neo-Morpheus WAN link)

With that given information, answer C (192.168.1.128-255/25) and answer F (192.168.1.0-3/30) best fit the scenario. Answers A, D, and E are incorrect because these are invalid subnet addresses. Answer B is incorrect because the /26 mask will only provide 64 IP addresses, which is not sufficient for the size of Network A. These addresses also overlap with the other office subnets.

4. C, E. IPv6 uses three types of communication: Unicast (one-to-one), Multicast (one-to-many), and Anycast (one-to-closest). Answer C is incorrect because the concept of Broadcast messaging is tied with the IPv4 protocol and is no longer valid in IPv6. Answer E is incorrect because there is no such thing as Cryptocast messaging.
5. A, B, D. An IPv6 address consists of eight octets that can be four hexadecimal characters each. Consecutive sets of zeros can be abbreviated with a double colon (::), but this can only be used once in each IP address. Leading zeros can also be dropped. Based on these rules, addresses from the question can be described as:

• 2001:0db8:0000:0000:0000:0000:1428:57ab (Valid, eight octets)
• 2001:0db8::1428:57ab (Valid, same address as above with abbreviation)
• 2001::1685:2123::1428:57ab (Invalid use of double colon)
• 2001:99:ab:1:99:2:1:9 (Valid, dropped leading zeros)
• 2001:1428:57ab:1685:2123: 1428:57ab (Invalid, only seven octets)
6. E. A dual-stack router can receive requests from both IPv4 and IPv6 clients on the same interface. This provides a smoother transition between the two protocols. Answers A, B, and D are incorrect because these all describe tunneling methods (IPv4 tunneled through an IPv6 network = 4to6). Answer C is incorrect because this describes a newer form of NAT that is able to translate between IPv4 and IPv6 addressing.
7. E, I. 10.170.120-123.0/24 breaks into the following binary equivalents:

• 10.170.120.0 = 00001010.10101010.01111000.00000000
• 10.170.121.0 = 00001010.10101010.01111001.00000000
• 10.170.122.0 = 00001010.10101010.01111010.00000000
• 10.170.123.0 = 00001010.10101010.01111011.00000000

Based on this, we can see that the first 22 bits of each subnet are the same, thus the summary address is 10.170.120.0/22 for Area 0 (answer E). 10.170.0-1.0/24 breaks into the following binary equivalents:

• 10.170.0.0 = 00001010.10101010. 00000000.00000000
• 10.170.1.0 = 00001010.10101010. 00000001.00000000

Based on this, we can see that the first 23 bits of each subnet are the same, thus the summary address is 10.170.0.0/23 (answer I). All other answers are not valid.

8. D. This subnet mask gives you four additional subnets using VLSM, with up to 14 hosts per subnetwork. Answer A is incorrect, as it is a higher subnet mask than your original /26, which is actually called supernetting. Answer B is incorrect because it is your original subnet mask. Answer C is incorrect, as it does not give you enough subnets. Answer E is incorrect, as it gives you enough subnets (six), but you would have only six hosts.
9. A, C, and D. A subnet mask of 255.255.255.240 divides the fourth octet into subnet parts: the highest four bits and a host port (the lowest four bits). You simply check the fourth octet to ensure that all subnet and host parts are okay. The host bit portion cannot be 0000 or 1111. Answers A, C, and D are correct because 33 in decimal is 00100001, 119 in decimal is 01110111, and 126 in decimal is 1111110. Answer B is incorrect, as 112 in decimal is 1110000 in binary. This is not a valid host address in this network. All its host bits are zero. Answer E is incorrect, as 175 in decimal is 10101111 in binary. All host bits are ones. This is the local broadcast address and cannot be used as a host address. Answer F is incorrect, as 208 in decimal is 11010000 in binary. This is not a valid host address in this network, and all its host bits are zero.
10. B, D, F. The departments will use the following subnet masks:

 Department Number of Users Subnet Mask Corporate 117 255.255.255.128 (126 hosts) Customer Support 15 255.255.255.224 (30 hosts) Financial 25 255.255.255.224 (30 hosts) HR 5 255.255.255.248 (6 hosts) Engineering 5 255.255.255.248 (6 hosts)

All other answers are invalid.

12. B. One of the IPv6 transition schemes includes an IPv6 to IPv4 (6to4) tunneling method. This allows you to tunnel your IPv6 networks through an IPv4 network. Answer A is incorrect because the VPN is actually using the IPv4 Internet as its connection point. Answer C is incorrect because 4to6 tunnels involve IPv4 networks tunneling through an IPv6 network. Answer D is incorrect because NAT-PT is a form of NAT that can handle translations between protocol suites. It is not related to VPN technology.
13. B, C. 172.16.112.0/24 and 172.16.113.0/24 can be summarized into the single entry 172.16.112.0/23. Answers A, D, and E represent addresses that cannot be summarized into a single routing entry that only encompasses two of the /24 network ranges.
14. B, C, E. RIPv2, EIGRP, and OSPF all support Variable Length Subnet Mask (VLSM) capabilities. Answers A and D are incorrect because RIPv1 and IGRP are classful routing protocols and do not support VLSM.
15. A. When auto-summarization is enabled, EIGRP will summarize networks back to their classful boundary anytime a discontiguous network is reached (such as the transition from 10.0.0.0/8 networks to 172.16.0.0/16 networks). In this case, R1 will summarize the corporate network back to 10.0.0.0/8 as it passes the routing update to R2. It will also summarize all the 172.16.x.x networks back to 172.16.0.0/16 as it passes the routing update into the corporate network. Answers B, C, and D are incorrect because auto-summarization only summarizes back to a classful boundary rather than to more specific subnet masks. Answer E is incorrect because EIGRP can handle VLSM with auto-summarization enabled.
16. D. IPv6 addresses have been expanded to 128-bit addressing from the 32-bit addressing of IPv4. This provides a virtually inexhaustible number of addresses (although, I'm sure many thought the same of the IPv4 address space). All other answers do not apply.
17. E. The Internet-valid addresses are considered "global" addresses in IPv6. They are specified to begin with 2000::/3. Answer A is incorrect because private addresses are for use in a private network, as it currently happens in IPv4 addressing. Answer B is incorrect because global addresses have replaced public addresses. Answers C and D do not apply directly to IPv6 addressing.
19. F. IPv6 addresses are assigned using the ipv6 address command. In IPv6, there is no decimal version of the subnet mask; all subnet masks are written in bit-notation. Answers A, C, and E are incorrect because they use the decimal version of the subnet mask. Answers B and D are incorrect because they use the incorrect command.
20. B. The exact syntax to enable the RIPng (RIP for IPv6) routing protocol is ipv6 router rip <tag>. The tag can be anything from a number to a name; in this question, the tag was "RIPng". This tag must be used when enabling RIP on an interface-by-interface basis. Answers A, C, and D will produce invalid syntax messages.
21. B, D, F, H. To perform the most efficient VLSM, always begin with the biggest subnet first. The ranges that will properly address the network in Figure 8.8 are as follows:

• Server Farm: 150.60.130.0-127/25 (answer H)
• College of Education: 150.60.130.128-159/27 (answer B)
• College of Business: 150.60.130.160-191/27 (answer F)

Answers A, C, E, and G are incorrect because they would each address a portion of the network but would not function correctly with the other given subnets.

22. The binary equivalents of the shown addresses are as follows, reflected in answer E:

 192.168.112.0 = 11000000.10101000.01110000.00000000 192.168.113.0 = 11000000.10101000.01110001.00000000 192.168.114.0 = 11000000.10101000.01110010.00000000 192.168.115.0 = 11000000.10101000.01110011.00000000 192.168.116.0 = 11000000.10101000.01110100.00000000 192.168.117.0 = 11000000.10101000.01110101.00000000 192.168.118.0 = 11000000.10101000.01110110.00000000 192.168.119.0 = 11000000.10101000.01110111.00000000

This shows that the first 21 bits of all these addresses are the same making the summary address 192.168.112.0/21. Answers A, B, and C are incorrect because 192.168.110.0 is an inaccurate starting point for the subnets. Answers D and F assume the wrong subnet mask.

23. The binary equivalents of the shown addresses are as follows, reflected in answer D:

 172.16.4.0 = 10101100.00010000.00000100.00000000 172.16.5.0 = 10101100.00010000.00000101.00000000 172.16.6.0 = 10101100.00010000.00000110.00000000 172.16.128.0 = 10101100.00010000.10000000.00000000

Because of the last subnet (172.16.128.0/24), a good summarization is not possible with these subnets. We must drop back to the classful summarization of 172.16.0.0/16. This helps demonstrate why discontiguous network addressing can destroy your network summarization efficiency. Answers A, B, and C are incorrect because the summarization addresses fail to encompass the 172.16.128.0/24 subnet.

24. D. The IP address 172.20.2.255/23 comes from the range of 172.20.2.0 through 172.30.3.255. The network ID 172.20.2.0 cannot be assigned to a host. The broadcast ID 172.20.3.255 cannot be assigned to a host. Everything in the middle of the range will function just fine. The other answers do not apply.
25. A, B, C. Given the 10.5.12.0/22 subnet, we can find the range of addresses to be 10.5.12.0 to 10.5.15.255. This makes Answers A, B, and C correct. Answers D and E are incorrect because they belong to the next subnet.
26. B. There are two ways of shortening an IPv6 address: removing a single group of consecutive zeros by using the double colon (::) and removing leading zeros from an octet. Answer B (2001:ab9:0:0:3::59ff:1ac5) shortens the octets by removing leading zeros and abbreviates the second group of consecutive zeros by using the ::. Answer A incorrectly uses a :: twice in the IPv6 address. Answer C has too many characters in one of the octets. Answer D uses the underscore character, which is invalid.
27. B. To find the number of valid host IP addresses, use the formula (2x) – 2, where "x" represents the number of host bits. In this case, the FastEthernet interface has the subnet mask 255.255.252.0, which uses 10 hosts bits. (210) – 2 = 1022. The other answers are not valid.
28. A. To enable the IPv6 protocol, use the command ipv6 unicast-routing from global configuration mode. All other answers produce an invalid syntax or incomplete command message.

Pearson IT Certification Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Pearson IT Certification and its family of brands. I can unsubscribe at any time.

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Pearson IT Certification products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

• Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
• Such marketing is consistent with applicable law and Pearson's legal obligations.
• Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
• Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.pearsonitcertification.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

• As required by law.
• With the consent of the individual (or their parent, if the individual is a minor)
• In response to a subpoena, court order or legal process, to the extent permitted or required by law
• To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
• In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
• To investigate or address actual or suspected fraud or other illegal activities
• To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
• To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
• To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.