- •Warning and Disclaimer
- •Feedback Information
- •Trademark Acknowledgments
- •About the Author
- •About the Technical Reviewers
- •Dedication
- •Acknowledgments
- •Contents at a Glance
- •Contents
- •Icons Used in This Book
- •Command Syntax Conventions
- •Cisco’s Motivation: Certifying Partners
- •Format of the CCNA Exams
- •What’s on the CCNA Exams
- •ICND Exam Topics
- •Cross-Reference Between Exam Topics and Book Parts
- •CCNA Exam Topics
- •INTRO and ICND Course Outlines
- •Objectives and Methods
- •Book Features
- •How This Book Is Organized
- •Part I: LAN Switching
- •Part II: TCP/IP
- •Part III: Wide-Area Networks
- •Part IV: Network Security
- •Part V: Final Preparation
- •Part VI: Appendixes
- •How to Use These Books to Prepare for the CCNA Exam
- •For More Information
- •Part I: LAN Switching
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Brief Review of LAN Switching
- •The Forward-Versus-Filter Decision
- •How Switches Learn MAC Addresses
- •Forwarding Unknown Unicasts and Broadcasts
- •LAN Switch Logic Summary
- •Basic Switch Operation
- •Foundation Summary
- •Spanning Tree Protocol
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Spanning Tree Protocol
- •What IEEE 802.1d Spanning Tree Does
- •How Spanning Tree Works
- •Electing the Root and Discovering Root Ports and Designated Ports
- •Reacting to Changes in the Network
- •Spanning Tree Protocol Summary
- •Optional STP Features
- •EtherChannel
- •PortFast
- •Rapid Spanning Tree (IEEE 802.1w)
- •RSTP Link and Edge Types
- •RSTP Port States
- •RSTP Port Roles
- •RSTP Convergence
- •Edge-Type Behavior and PortFast
- •Link-Type Shared
- •Link-Type Point-to-Point
- •An Example of Speedy RSTP Convergence
- •Basic STP show Commands
- •Changing STP Port Costs and Bridge Priority
- •Foundation Summary
- •Foundation Summary
- •Virtual LANs and Trunking
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Review of Virtual LAN Concepts
- •Trunking with ISL and 802.1Q
- •ISL and 802.1Q Compared
- •VLAN Trunking Protocol (VTP)
- •How VTP Works
- •VTP Pruning
- •Foundation Summary
- •Part II: TCP/IP
- •IP Addressing and Subnetting
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •IP Addressing Review
- •IP Subnetting
- •Analyzing and Interpreting IP Addresses and Subnets
- •Math Operations Used to Answer Subnetting Questions
- •Converting IP Addresses from Decimal to Binary and Back Again
- •The Boolean AND Operation
- •How Many Hosts and How Many Subnets?
- •What Is the Subnet Number, and What Are the IP Addresses in the Subnet?
- •Finding the Subnet Number
- •Finding the Subnet Broadcast Address
- •Finding the Range of Valid IP Addresses in a Subnet
- •Finding the Answers Without Using Binary
- •Easier Math with Easy Masks
- •Which Subnet Masks Meet the Stated Design Requirements?
- •What Are the Other Subnet Numbers?
- •Foundation Summary
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Extended ping Command
- •Distance Vector Concepts
- •Distance Vector Loop-Avoidance Features
- •Route Poisoning
- •Split Horizon
- •Split Horizon with Poison Reverse
- •Hold-Down Timer
- •Triggered (Flash) Updates
- •RIP and IGRP
- •IGRP Metrics
- •Examination of RIP and IGRP debug and show Commands
- •Issues When Multiple Routes to the Same Subnet Exist
- •Administrative Distance
- •Foundation Summary
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Link-State Routing Protocol and OSPF Concepts
- •Steady-State Operation
- •Loop Avoidance
- •Scaling OSPF Through Hierarchical Design
- •OSPF Areas
- •Stub Areas
- •Summary: Comparing Link-State and OSPF to Distance Vector Protocols
- •Balanced Hybrid Routing Protocol and EIGRP Concepts
- •EIGRP Loop Avoidance
- •EIGRP Summary
- •Foundation Summary
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Route Summarization and Variable-Length Subnet Masks
- •Route Summarization Concepts
- •VLSM
- •Route Summarization Strategies
- •Sample “Best” Summary on Seville
- •Sample “Best” Summary on Yosemite
- •Classless Routing Protocols and Classless Routing
- •Classless and Classful Routing Protocols
- •Autosummarization
- •Classful and Classless Routing
- •Default Routes
- •Classless Routing
- •Foundation Summary
- •Advanced TCP/IP Topics
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Scaling the IP Address Space for the Internet
- •CIDR
- •Private Addressing
- •Network Address Translation
- •Static NAT
- •Dynamic NAT
- •Overloading NAT with Port Address Translation (PAT)
- •Translating Overlapping Addresses
- •Miscellaneous TCP/IP Topics
- •Internet Control Message Protocol (ICMP)
- •ICMP Echo Request and Echo Reply
- •Destination Unreachable ICMP Message
- •Time Exceeded ICMP Message
- •Redirect ICMP Message
- •Secondary IP Addressing
- •FTP and TFTP
- •TFTP
- •MTU and Fragmentation
- •Foundation Summary
- •Part III: Wide-Area Networks
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Review of WAN Basics
- •Physical Components of Point-to-Point Leased Lines
- •Data-Link Protocols for Point-to-Point Leased Lines
- •HDLC and PPP Compared
- •Looped Link Detection
- •Enhanced Error Detection
- •Authentication Over WAN Links
- •PAP and CHAP Authentication
- •Foundation Summary
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •ISDN Protocols and Design
- •Typical Uses of ISDN
- •ISDN Channels
- •ISDN Protocols
- •ISDN BRI Function Groups and Reference Points
- •ISDN PRI Function Groups and Reference Points
- •BRI and PRI Encoding and Framing
- •PRI Encoding
- •PRI Framing
- •BRI Framing and Encoding
- •DDR Step 1: Routing Packets Out the Interface to Be Dialed
- •DDR Step 2: Determining the Subset of the Packets That Trigger the Dialing Process
- •DDR Step 3: Dialing (Signaling)
- •DDR Step 4: Determining When the Connection Is Terminated
- •ISDN and DDR show and debug Commands
- •Multilink PPP
- •Foundation Summary
- •Frame Relay
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Frame Relay Protocols
- •Frame Relay Standards
- •Virtual Circuits
- •LMI and Encapsulation Types
- •DLCI Addressing Details
- •Network Layer Concerns with Frame Relay
- •Layer 3 Addressing with Frame Relay
- •Frame Relay Layer 3 Addressing: One Subnet Containing All Frame Relay DTEs
- •Frame Relay Layer 3 Addressing: One Subnet Per VC
- •Frame Relay Layer 3 Addressing: Hybrid Approach
- •Broadcast Handling
- •Frame Relay Service Interworking
- •A Fully-Meshed Network with One IP Subnet
- •Frame Relay Address Mapping
- •A Partially-Meshed Network with One IP Subnet Per VC
- •A Partially-Meshed Network with Some Fully-Meshed Parts
- •Foundation Summary
- •Part IV: Network Security
- •IP Access Control List Security
- •“Do I Know This Already?” Quiz
- •Foundation Topics
- •Standard IP Access Control Lists
- •IP Standard ACL Concepts
- •Wildcard Masks
- •Standard IP ACL: Example 2
- •Extended IP Access Control Lists
- •Extended IP ACL Concepts
- •Extended IP Access Lists: Example 1
- •Extended IP Access Lists: Example 2
- •Miscellaneous ACL Topics
- •Named IP Access Lists
- •Controlling Telnet Access with ACLs
- •ACL Implementation Considerations
- •Foundation Summary
- •Part V: Final Preparation
- •Final Preparation
- •Suggestions for Final Preparation
- •Preparing for the Exam Experience
- •Final Lab Scenarios
- •Scenario 1
- •Scenario 1, Part A: Planning
- •Solutions to Scenario 1, Part A: Planning
- •Scenario 2
- •Scenario 2, Part A: Planning
- •Solutions to Scenario 2, Part A: Planning
- •Part VI: Appendixes
- •Glossary
- •Answers to the “Do I Know This Already?” Quizzes and Q&A Questions
- •Chapter 1
- •“Do I Know This Already?” Quiz
- •Chapter 2
- •“Do I Know This Already?” Quiz
- •Chapter 3
- •“Do I Know This Already?” Quiz
- •Chapter 4
- •“Do I Know This Already?” Quiz
- •Chapter 5
- •“Do I Know This Already?” Quiz
- •Chapter 6
- •“Do I Know This Already?” Quiz
- •Chapter 7
- •“Do I Know This Already?” Quiz
- •Chapter 8
- •“Do I Know This Already?” Quiz
- •Chapter 9
- •“Do I Know This Already?” Quiz
- •Chapter 10
- •“Do I Know This Already?” Quiz
- •Chapter 11
- •“Do I Know This Already?” Quiz
- •Chapter 12
- •“Do I Know This Already?” Quiz
- •Using the Simulation Software for the Hands-on Exercises
- •Accessing NetSim from the CD
- •Hands-on Exercises Available with NetSim
- •Scenarios
- •Labs
- •Listing of the Hands-on Exercises
- •How You Should Proceed with NetSim
- •Considerations When Using NetSim
- •Routing Protocol Overview
- •Comparing and Contrasting IP Routing Protocols
- •Routing Through the Internet with the Border Gateway Protocol
- •RIP Version 2
- •The Integrated IS-IS Link State Routing Protocol
- •Summary of Interior Routing Protocols
- •Numbering Ports (Interfaces)
532Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Questions
14.Imagine that host 10.1.1.1 in Figure 8-21 sends a packet to the server at 170.1.1.1 and that the NAT router also happens to fragment the packet. Inside the context of this network, explain how reassembly of the fragments into the original packet occurs.
Answer: The endpoint host for which the packets are destined always reassembles the fragments. In this case, host 170.1.1.1 reassembles the packet.
15.Imagine that R1 has an interface, FastEthernet 0/0, that uses ISL trunking to a switch. R1 needs to route between VLAN 1 and VLAN 2. Create a valid router configuration.
Answer:
interface fastethernet 0/0.1
ip address 10.1.1.1 255.255.255.0 encapsulation isl 1
!
interface fastethernet 0/0.2
ip address 10.1.2.1 255.255.255.0 encapsulation isl 2
16.Describe how NAT overload manages to support more than one inside local IP address using a single inside global address.
Answer: NAT overload uses Port Address Translation (PAT) to essentially translate both the source address and port numbers for incoming inside packets. By allocating unique port numbers to be used with a single inside global IP address, NAT overload can make multiple sockets on multiple inside hosts appear to be multiple sockets, but from a single host, on the public part of the network.
Chapter 9
“Do I Know This Already?” Quiz
1.Which of the following types of WAN connections allow the direct use of PPP as the encapsulation type on the interface?
Answer: A, C
2.Which of the following commands are required on the router connected to a DTE cable to make the serial link between two routers work when the two routers are connected in a lab using a DTE and DCE cable and no CSU/DSUs?
Answer: E. None of these commands is needed at the DTE. The clock rate 56000 command, or one like it, is needed on the router with a DCE cable.
3.Which of the following commands make a serial interface revert to the default data-link protocol if it is currently configured with PPP?
Answer: E, G. HDLC is the default setting.
Chapter 9 533
4.Which of the following authentication protocols authenticates a device on the other end of a link without sending any password information in clear text?
Answer: C. Of these answers, only PAP and CHAP are authentication protocols. PAP sends the password in clear text.
5.Imagine that two routers, R1 and R2, have a leased line between them. Each router had its configuration erased and was then reloaded. R1 was then configured with the following commands:
interface s0/0 encapsulation ppp
ppp authentication chap
Which of the following configuration commands can complete the configuration on R1 so that CHAP can work correctly? Assume that R2 has been configured correctly and that the password is fred.
Answer: D. R1 needs to know the password associated with the router on the other end of the link—namely, R2.
6.Which of the following is a reason to avoid using link compression?
Answer: C. “Reducing” available CPU cycles is an odd way to say that compression uses CPU in the router, which is one reason to choose not to perform compression.
7.Which of the following does PPP use as part of how it notices when a link has been looped, causing packets sent by a router to be returned to that router?
Answer: B
8.Which of the following are protocols defined as part of PPP?
Answer: B, D
Q&A
1.Define the terms DCE and DTE in the context of the physical layer and a point-to-point serial link.
Answer: At the physical layer, DTE refers to the device that looks for clocking from the device on the other end of the cable on a link. The DCE supplies that clocking. For example, the computer is typically the DTE, and the modem or CSU/DSU is the DCE. At the data link layer, both X.25 and Frame Relay define a logical DTE and DCE. In this case, the customer premises equipment (CPE), such as a router and CSU/DSU, is the logical DTE, and the service provider equipment (the Frame Relay switch and CSU/ DSU) is the DCE.
534Appendix A: Answers to the “Do I Know This Already?” Quizzes and Q&A Questions
2.Identify the command used to set the clock rate on an interface in which a DCE cable has been inserted. Compare and contrast the two styles of the command that may be entered in configuration mode versus which style shows up in the configuration.
Answer: The clock rate command and the clockrate command both set the rate at which an interface clocks over a serial DCE cable. When you ask for help while in interface configuration mode, the clock rate command is shown, but help does not list the clockrate command. However, after you issue the command, a show running-config lists the clockrate command under the interface, regardless of which of the two commands was entered in configuration mode.
3.Name one WAN data-link protocol used on point-to-point leased lines that defines a method of announcing the interface’s IP addresses to other devices attached to the WAN.
Answer: PPP uses an IP Control Protocol (IPCP) to announce, and sometimes assign, IP addresses to each end of the link.
4.Can PPP dynamically assign IP addresses? If so, is this feature always enabled?
Answer: PPP’s IPCP protocol can assign an IP address to the device on the other end of the link. This process is not required and is not performed by default. PPP usually does address assignment for dial access, such as when a user dials an Internet service provider.
5.Create a configuration to enable PPP on serial 0 for IP. Make up IP Layer 3 addresses as needed.
interface serial 0
ip addr 1.1.1.1 255.255.255.0 encapsulation ppp
Answer: encapsulation ppp is all that is needed for PPP.
6.Define the terms PAP and CHAP. Which one sends passwords in clear-text format?
Answer: PAP stands for Password Authentication Protocol. CHAP stands for Challenge Handshake Authentication Protocol. PAP sends passwords as simple text, whereas CHAP uses MD5 hashing to protect the password contents.
7.CHAP configuration uses names and passwords. Given Routers A and B, describe what names and passwords must match in the respective CHAP configurations.
Answer: Router A has name B and a corresponding password configured. Router B has name A and the same password configured. The names used are the host names of the routers unless the CHAP name is configured.
Chapter 9 535
8.What field has Cisco added to the HDLC header, making it proprietary?
Answer: A Protocol Type field has been added to allow support for multiprotocol traffic. HDLC was not originally designed to allow for multiprotocol support.
9.List the types of packet switching mentioned in this chapter. Identify the one for which all traffic is segmented into smaller pieces.
Answer: Frame Relay, X.25, and ATM were all mentioned as packet switching services. ATM, also called cell switching, segments all traffic into 53-byte cells before transmission and reassembles the cells into the original frame after they are through the WAN.
10.Two-wire leased circuits are seldom used today, and certainly not between two routers. What problem was solved with the advent of four-wire leased circuits versus two-wire?
Answer: Two-wire leased lines could be used as each single pair, for transmission in only one direction at a time. With a four-wire circuit, each pair could be used for transmission in a different direction, allowing full-duplex data transmission.
11.Define synchronous in relation to leased lines.
Answer: The imposition of time ordering on a bit stream. Practically speaking, a device tries to use the same speed as another device on the other end of a serial link. However, by examining transitions between voltage states on the link, the device can notice slight variations in the speed on each end and can adjust its speed accordingly.
12.Create a CHAP configuration between two routers. Make up specific details as needed.
Answer: Your configuration will probably be a little different from the one shown here. To be correct, you need the username global commands that refer to the other router’s host name, with correct case and the same password on each side. PPP must be enabled on each serial link, and ppp authentication chap must be on each interface.
Router Fred |
Router Barney |
username Barney password Bedrock |
username Fred password Bedrock |
! |
! |
interface serial 0 |
interface serial 0 |
encapsulation ppp |
encapsulation ppp |
ppp authentication chap |
ppp authentication chap |
. |
. |