
- •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)

212 Chapter 6: OSPF and EIGRP Concepts and Configuration
Foundation Summary
The “Foundation Summary” section lists the most important facts from the chapter. Although this section does not list everything that will be on the exam, a well-prepared CCNA candidate should at a minimum know all the details in each Foundation Summary before taking the exam.
The basic process of learning routes for the first time with OSPF goes something like this:
1.Each router discovers its neighbors on each interface. The list of neighbors is kept in a neighbor table.
2.Each router uses a reliable protocol to exchange topology information (LSAs) with its neighbors.
3.Each router places the learned topology information in its topology database.
4.Each router runs the SPF algorithm against its own topology database to calculate the best routes to each subnet in the database.
5.Each router places the best route to each subnet in the IP routing table.
Figure 6-9 shows a network with multiple areas, along with the perspective of the topology for routers inside Area 1.

Foundation Summary 213
Figure 6-9 Two-Area OSPF
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Area 0 |
Area 1 |
(Backbone Area) |
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Area |
6 |
10.1.6.0 |
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2 |
Border |
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Router |
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10.1.7.0 |
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7 |
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1 |
3 |
5 |
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10.1.8.0 |
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8 |
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4 |
10.1.9.0 |
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9 |
2 |
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10.1.6.0 |
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10.1.7.0 |
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1 |
3 |
10.1.8.0 |
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10.1.9.0 |
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4 |
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Table 6-8 summarizes some of the key points of comparison between the two types of routing protocols.
Table 6-8 Comparing Link-State and Distance Vector Protocols
Feature |
Link State |
Distance Vector |
|
|
|
Convergence Time |
Fast |
Slow, mainly because of loop- |
|
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avoidance features |
|
|
|
Loop Avoidance |
Built into the protocol |
Requires extra features such as split |
|
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horizon |
|
|
|
Memory and CPU |
Can be large; good |
Low |
Requirements |
design can minimize |
|
|
|
|
Requires Design Effort for |
Yes |
No |
Larger Networks |
|
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|
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|
Public Standard or Proprietary |
OSPF is public |
RIP is publicly defined; IGRP is not |
|
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|

214 Chapter 6: OSPF and EIGRP Concepts and Configuration
Table 6-9 summarizes some of the key comparison points between EIGRP, IGRP, and OSPF.
Table 6-9 |
EIGRP Features Compared to OSPF and IGRP |
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|
|
Feature |
EIGRP |
IGRP |
OSPF |
|
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|
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|
Discovers neighbors before exchanging routing information |
Yes |
No |
Yes |
|
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|
Builds some form of topology table in addition to adding routes |
Yes |
No |
Yes |
|
to the routing table |
|
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|
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|
Converges quickly |
Yes |
No |
Yes |
|
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|
|
|
|
Uses metrics based on bandwidth and delay by default |
Yes* |
Yes |
No |
|
Sends full routing information on every routing update cycle |
No |
Yes |
No |
|
|
|
|
|
|
Requires distance vector loop-avoidance features |
No |
Yes |
No |
|
|
|
|
|
|
Public standard |
No |
No |
Yes |
|
|
|
|
|
*EIGRP uses the same metric as IGRP, except that EIGRP scales the metric by multiplying by 256.
Example 6-6 shows two alternative OSPF configurations for a router. All interfaces are in Area 0.
Example 6-6 OSPF Single-Area Configuration Alternatives
interface ethernet 0/0
ip address 10.1.1.1 255.255.255.0 interface serial 0/0
ip address 10.1.4.1 255.255.255.0 interface serial 0/1
ip address 10.1.6.1 255.255.255.0
!
router ospf 1
network 10.0.0.0 0.255.255.255 area 0
!
! Alternately:
!
router ospf 1
network 10.1.1.1 0.0.0.0 area 0 network 10.1.4.1 0.0.0.0 area 0 network 10.1.6.1 0.0.0.0 area 0
The wildcard mask represents a 32-bit number. When the mask has a binary 1 in one of the bit positions, that bit is considered a wildcard bit, meaning that the router should not care what binary value is in the corresponding numbers. For that reason, binary 1s in the wildcard mask are called don’t care bits. If the wildcard mask bit is 0 in a bit position, the

Foundation Summary 215
corresponding bits in the numbers being compared must match. You can think of these bits as the do care bits. The router must examine the two numbers and make sure that the values match for the bits that matter—in other words, the do care bits.
For instance, the first wildcard mask in Example 6-6 is 0.255.255.255. When converted to binary, this number is 0000 0000 1111 1111 1111 1111 1111 1111—in other words, eight 0s and 24 1s. The network command tells the IOS to compare 10.0.0.0, which is the number in the network command, to the IP addresses of each interface on the router. The wildcard mask tells IOS to compare only the first octet; the last three octets are wildcards, and anything matches. So, all three interface IP addresses are matched.
With the wildcard mask of 0.0.0.0, entire numbers must be compared—hence the specific network commands referring to the specific IP addresses of the interfaces in the alternative configuration.

216 Chapter 6: OSPF and EIGRP Concepts and Configuration
Q&A
As mentioned in the Introduction, you have two choices for review questions. The following questions give you a bigger challenge than the exam because they are open-ended. By reviewing with this more-difficult question format, you can exercise your memory better and prove your conceptual and factual knowledge of the topics covered in this chapter. The answers to these questions are found in Appendix A.
For more practice with exam-like question formats, including multiple-choice questions and those using a router simulator, use the exam engine on the CD.
1.Create a minimal configuration enabling IP on each interface on a 2600 series router (two serial, one Ethernet). The Network Information Center (NIC) assigns you network 192.168.1.0. Your boss says that you need, at most, 60 hosts per LAN subnet. You also have point-to-point links attached to the serial interfaces. When choosing the IP address values and subnet numbers, you decide to start with the lowest numerical values. Assume that point-to-point serial links will be attached to this router and that EIGRP is the routing protocol.
2.Write down the steps you would take to migrate from RIP to OSPF in a router whose current RIP configuration includes only router rip followed by a network 10.0.0.0 command. Assume a single OSPF area, and use as few network commands as possible.
3.Create a configuration for EIGRP on a router with these interfaces and addresses: e0 using 10.1.1.1, e1 using 224.1.2.3, s0 using 10.1.2.1, and s1 using 199.1.1.1. Use process ID 5.
4.Create a configuration for EIGRP on a router with these interfaces and addresses: e0 using 200.1.1.1, e1 using 128.1.3.2, s0 using 192.0.1.1, and s1 using 223.254.254.1.
5.From a router’s user mode, without using debugs or privileged mode, how can you determine what routers are sending you EIGRP routing updates?
6.If the command router eigrp 1, followed by network 10.0.0.0, with no other network commands, is configured in a router that has an Ethernet0 interface with IP address 168.10.1.1, does EIGRP send updates out Ethernet0?
7.If the command router ospf 1, followed by network 10.0.0.0 0.255.255.255 area 0, with no other network commands, is configured in a router that has an Ethernet0 interface with IP address 10.10.1.1, does OSPF send updates out Ethernet0?

Q&A 217
8.If the commands router eigrp 1 and network 10.0.0.0 are configured in a router that has an Ethernet0 interface with IP address 168.10.1.1, mask 255.255.255.0, does this router have a route to 168.10.1.0?
9.Which command lists all IP routes learned via OSPF?
10.Compare and contrast the type of information exchanged in routing updates sent by distance vector routing protocols versus link-state protocols.
11.Define balanced hybrid and give an example of a balanced hybrid protocol.
12.Describe how balanced hybrid protocols differ from distance vector protocols in terms of how a router notices that a neighboring router has failed.
13.List the distance vector loop-avoidance features used by OSPF, such as split horizon.
14.List two OSPF features that help decrease the size of the OSPF topology database.
15.Assume that you must choose between OSPF and EIGRP for a routing protocol in a new network you are building. List and explain the most compelling reason to choose OSPF and the most compelling reason to choose EIGRP.

This chapter covers the following subjects:
■Route Summarization and VariableLength Subnet Masks
■Classless Routing Protocols and Classless Routing