C H A P T E R 8

Advanced TCP/IP Topics

TCP/IP is undoubtedly the most important protocol suite in the networking world today. In the last few chapters, the coverage of TCP/IP has focused on issues related to routing protocols. However, other TCP/IP topics are important for the ICND exam as well. This chapter covers a variety of TCP/IP topics, some related and some totally unrelated—but all important.

This chapter starts by covering several topics related to improving IP addressing scalability. Classless Interdomain Routing (CIDR) reduces the size of Internet routing tables, much like route summarization, but specifically for routes in the Internet. Private addressing used with Network Address Translation (NAT) reduces the need for each company to have its own entire Class A, B, and C registered networks when connecting to the Internet, thereby delaying the day when the world runs out of registered IP addresses.

The second section of this chapter covers several unrelated topics, including ICMP, secondary IP addresses, FTP and TFTP, fragmentation, and routing between VLANs.

If you’re studying for the CCNA exam, the single-exam method of getting your CCNA certification, you might be using both of my books, following the reading plan outlined in the Introduction to both books. If so, review your reading plan, and note that after this chapter, you should go back to CCNA INTRO Exam Certification Guide and pick up with Chapter 15, “Remote Access Technologies.”

“Do I Know This Already?” Quiz

The purpose of the “Do I Know This Already?” quiz is to help you decide if you need to read the entire chapter. If you intend to read the entire chapter, you do not necessarily need to answer these questions now.

The 14-question quiz, derived from the major sections in the “Foundation Topics” section, helps you determine how to spend your limited study time.

252 Chapter 8: Advanced TCP/IP Topics

Table 8-1 outlines the major topics discussed in this chapter and the “Do I Know This Already?” quiz questions that correspond to those topics.

Table 8-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

CAUTION The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you don’t know the answer to a question or you’re only partially sure of the answer, you should mark this question as wrong for purposes of the self-assessment. Giving yourself credit for an answer you guess correctly skews your self-assessment results and might give you a false sense of security.

1.What does CIDR stand for?

a.Classful IP Default Routing

b.Classful IP D-class Routing

c.Classful Interdomain Routing

d.Classless IP Default Routing

e.Classless IP D-class Routing

f.Classless Interdomain Routing

2.Which of the following summarized subnets are valid routes according to the main purpose of CIDR?

a.10.0.0.0 255.255.255.0

b.10.1.0.0 255.255.0.0

c.200.1.1.0 255.255.255.0

d.200.1.0.0 255.255.0.0

3.Which of the following are not private addresses according to RFC 1918?

a.172.31.1.1

b.172.33.1.1

c.10.255.1.1

d.10.1.255.1

e.191.168.1.1

“Do I Know This Already?” Quiz 253

4.With static NAT, performing translation for inside addresses only, what causes NAT table entries to be created?

a.The first packet from the inside network to the outside network

b.The first packet from the outside network to the inside network

c.Configuration using the ip nat inside source command

d.Configuration using the ip nat outside source command

5.With dynamic NAT, performing translation for inside addresses only, what causes NAT table entries to be created?

a.The first packet from the inside network to the outside network

b.The first packet from the outside network to the inside network

c.Configuration using the ip nat inside source command

d.Configuration using the ip nat outside source command

6.Which of the following commands identifies the inside local IP addresses when using dynamic NAT to translate only the source addresses of packets from a private network number?

a.ip nat inside source list 1 pool barney

b.ip nat pool barney 200.1.1.1 200.1.1.254 netmask 255.255.255.0

c.ip nat inside

d.ip nat inside 200.1.1.1 200.1.1.2

e.None of the above

7.Which of the following commands identifies the outside local IP addresses when using dynamic NAT to translate only the source addresses of packets from a private network number?

a.ip nat inside source list 1 pool barney

b.ip nat pool barney 200.1.1.1 200.1.1.254 netmask 255.255.255.0

c.ip nat inside

d.ip nat inside 200.1.1.1 200.1.1.2

e.None of the above

254Chapter 8: Advanced TCP/IP Topics

8.Imagine that an Ethernet interface on a router has already been configured with IP address 10.1.1.1, mask 255.255.255.0. Which of the following commands adds a secondary IP address to the interface?

a.ip address 10.1.1.2 255.255.255.0

b.ip address 10.1.1.254 255.255.255.0

c.ip address 10.1.2.1 255.255.255.0

d.secondary ip address 10.1.2.1 255.255.255.0

e.ip secondary address 10.1.2.1 255.255.255.0

f.ip secondary 10.1.2.1 255.255.255.0

g.ip address 10.1.2.1 255.255.255.0 secondary

9.Which of the following file transfer protocols, defined in various Internet RFCs, provides the most features?

a.FTP

b.TFTP

c.FTPO

d.BFTP

10.Imagine that Fred is a PC attached to an Ethernet, and that its default router, R1, is attached to the same Ethernet. R1 has a point-to-point serial link to R2, which has an Ethernet attached, to which PC Barney is attached. The MTU of each Ethernet has the default value. What must be true for R1 to fragment packets sent from Fred to Barney?

a.The serial link’s MTU must be less than 1500.

b.The serial link’s MTU must be less than 1518.

c.The serial link’s MTU must be less than 1526.

d.R1 must have the fragment on command configured on the serial interface.

“Do I Know This Already?” Quiz 255

11.Router1 has a FastEthernet interface 0/0 with IP address 10.1.1.1. The interface is connected to a switch. This connection is then migrated to ISL. Which of the following commands could be useful to configure Router1 for ISL?

a.interface fastethernet 0/0.4

b.isl enable

c.isl enable 4

d.trunking enable

e.trunking enable 4

f.encapsulation isl

g.encapsulation isl 4

12.What is the meaning of “.” in the output of a ping command?

a.The ping worked.

b.The ping did not work because an echo request could not be sent.

c.The ping did not work because an echo reply was not received.

d.The ping did not work because an ICMP message was returned implying that the lifetime was exceeded.

e.The ping did not work because an ICMP message was returned implying that there was no route to the subnet.

13.What is the meaning of “U” in the output of a ping command?

a.The ping worked.

b.The ping did not work because an echo request could not be sent.

c.The ping did not work because an echo reply was not received.

d.The ping did not work because an ICMP message was returned implying that the lifetime was exceeded.

e.The ping did not work because an ICMP message was returned implying that there was no route to the subnet.

14.What ICMP message code(s) does the trace command rely on?

a.Host Unreachable

b.Subnet Unreachable

c.Time to Live Exceeded

d.Can’t Fragment

256 Chapter 8: Advanced TCP/IP Topics

The answers to the “Do I Know This Already?” quiz appear in Appendix A. The suggested choices for your next step are as follows:

■11 or less overall score—Read the entire chapter. This includes the “Foundation Topics,” “Foundation Summary,” and “Q&A” sections.

■12, 13, or 14 overall score—If you want more review on these topics, skip to the “Foundation Summary” section and then go to the “Q&A” section. Otherwise, move to the next chapter.