Designing IP Networks

8 Mar

This chapter covers the following topics, which you need to understand to pass the CCNP/CCDP/CCIP BSCI exam:

■ Criteria in designing IP networks

■ Private addresses on the Internet

■ Connecting to the outside world with NAT

■ Understanding IPv6

C H A P T E R 3
Designing IP Networks

This chapter deals with designing IP networks to efficiently use the addressing structure to reduce the routing tables and thus conserve network resources. Many of the design principles for an IP network were dealt with in Chapter 2, “IP Addressing.” The approach in Chapter 2 was a practical one, explaining how to address a network and the need for a hierarchical design. By contrast, this chapter examines the design criteria from a highlevel perspective. Instead of describing how you would design a hierarchical addressing scheme to support variable-length subnet masks (VLSM) and allow summarization, this chapter explains why there is a need for hierarchical structure and summarization.
This chapter also considers the relatively recent solution to the problem of applying for limited Internet addresses from the IANA, private addressing. When using private addresses, any connection to the Internet must be handled in such a way that duplicate addresses do not appear in the public domain. Duplicate addresses result in a lack of connectivity. Solutions to the problem of duplicate addressing are explored within this chapter. IPv6 and its features are discussed in terms of network design and implementation. In particular, the advantages of IPv6 over IPv4 are considered. The IPv6 addressing format is also explained  as are the various methods of transitioning an IPv4 network to run IPv6 and the routing protocols that are available for the new IP stack.

“Do I Know This Already?” Quiz
The purpose of the “Do I Know This Already?” quiz is to help you decide what parts of this chapter to use. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now. The 15-question quiz, derived from the major sections in the “Foundation Topics” portion of the chapter, helps you to determine how to spend your limited study time.

86 Chapter 3: Designing IP Networks
Table 3-1 outlines the major topics discussed in this chapter and the “Do I Know This Already?” quiz questions that correspond to those topics. Table 3-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

NOTE: The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer, you should mark this question wrong for purposes of the self-assessment. Giving yourself credit for an answer you correctly guess skews your self-assessment results and might provide you with a false sense of security.

1. Which of the following are valid uses for access lists?
a. Restricting networks sent out in routing updates
b. Restricting connectivity to remote networks
c. Preventing users interactive access to the routing table
d. Restricting large packet sizes from traversing the network
2. In the hierarchical design suggested by Cisco, at which layer are access lists not recommended?
a. Core layer
b. Access layer
c. Distribution layer
d. Access lists are recommended at all layers
3. What is the function of the distribution layer?
a. Connects the routers to the end systems, allowing the datagrams to be distributed to the destination address
b. Distributes the datagrams to the rest of the network. It is the pinnacle of the network, connecting the other layers to one another.
c. Provides the demarcation point between the core and access layers, providing policybased connectivity and allowing you to do packet manipulation

d. Provides the connections to other autonomous systems or to the Internet, distributing data
to the outside world
4. What feature is required in a routing protocol to allow it to support prefix routing?
a. Interoperability with other vendors
b. The extended prefix or subnet mask is sent in the routing update.
c. Hierarchical addressing
d. The protocol must be VLSM compliant.
5. In order for a network to support summarization, which of the following must be true?
a. VLSM needs to be configured on the DHCP server.
b. The addresses to be summarized share the same high order bits.
c. The physical and logical topology of the network is hierarchical.
d. The design of the network must conform to the rules laid out in RFC 2011.
6. In designing the IP addressing of a network, which of the following questions are pertinent to the design process?
a. How many subnets exist currently in your network?
b. Is access to the subnets required from other subnets?
c. Are you running PCSA?
d. Where are the subnets in relation to the topology map?
7. What are the private addresses allocated in RFC 1918?

a. Class A:
b. Class A:, Class B:, Class C:
c. Class A:, Class B:–, Class C:–
d. Class A:, Class B:–, Class C:–
8. What is the purpose of private addressing?
a. To allow companies to have no communication with the Internet
b. To allow companies to address the networks within their autonomous system without any constraint on limited IP address space on the Internet
c. To configure encryption on individual end systems
d. To prevent spam attacks

Chapter 3: Designing IP Networks
9. Is it necessary to prevent the private addresses from entering the Internet?
a. Yes, if the private addresses appear on the Internet, the packet with the address should be
b. Yes, the private address would invite unsolicited mail.
c. No, the private address is unique to the Internet; it simply indicates that there is a firewall
in place.
d. No, the destination address will convert the source address to a unique address.
10. Which NAT feature would you implement if you wished to create a one-to-one translation?
a. Dynamic Source Address Translation
b. Port Address Translation
c. Static Addressing
d. Destination address rotary translation
11. Which of the following most closely defines a feature of NAT?
a. To translate an address on one network into a different address for another network
b. To encrypt the source address to prevent spam attacks
c. To translate private addresses for use in a WINS server
d. To store prefix routing information on the Internet

12. Which of the following is a feature of NAT that is supported by Cisco?
a. Encryption
b. Destination Allocation Resource Translation
c. Port Allocation Translation
d. Port Address Translation
13. Which of the following is a valid IPv6 address?
a. 4021::240E::0AC0:3428:121C
b. 4021:240E::0AC0:3428::
c. 4021::0000::240E::0000::0000::0AC0::3428::121C
d. 4021:0:240E::0AC0:3428:121C

14. How long is an IPv6 address?
a. 16 hexadecimal numbers
b. 32 decimal numbers
c. 128 bits
d. 32 bits
15. The multicast address range for IPv6 is which of the following?
a. F000::/8 – FF0F::/8
b. FF00::/8 – FFFF::/8
c. F000::/8 – FFFF::/8
d. FF00::/8 – FF0F::/8
The answers to the “Do I Know This Already?” quiz are found in Appendix A, “Chapter ‘Do I Know This Already?’ Quizzes and Q&A Sections.” The suggested choices for your next step are as
■ 8 or less overall score —Read the entire chapter. This includes the “Foundation Topics” and “Foundation Summary” sections, the “Q&A” section, and the “Scenarios” at the end of the chapter.
■ 9–12 overall score —Begin with the “Foundation Summary” section, and then go to the “Q&A” section and the “Scenarios” at the end of the chapter. If you have trouble with these exercises, read the appropriate sections in “Foundation Topics.”
■ 13 or more overall score —If you want more review on these topics, skip to the “Foundation Summary” section, and then go to the “Q&A” section and the “Scenarios” at the end of the chapter. Otherwise, move to the next chapter.

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