Auto Summary and Route Aggregation
The IOS is optimized to perform routing as fast as possible. Most of the Layer 3 routing performance improvement in the brief history of routers has been through improved algorithms many times those improved algorithms later have been implemented in hardware to provide additional latency improvements. Although these improvements have been a great benefit, it is typically true that any algorithm that searches a list will run more quickly if the list is short, compared to searching a similar list...
RIP1 and IGRPNo Subnet Masks
RIP-1 and IGRP do not transmit the subnet mask in the routing updates, as seen in the debug output examples in this section. As a CCNA, Cisco expects you to be able to articulate the implications of the missing mask to the function of the routing protocol. Several subtle actions are taken in light of the lack of mask information in the update Updates sent out an interface in network X, when containing routes about subnets of network X, contain the subnet numbers of the subnets of network X but...
About the Author
Wendell Odom has worked with networking technology for 15 years. He is currently a Cisco Systems Senior Systems Engineer in the Atlanta, Georgia office, assigned to several large Cisco customers. Prior to joining Cisco in 1999, Wendell provided consulting services on large networks as well as training services. He spent his first eight years in networking working for IBM, helping customers evolve their SNA networks into multiprotocol networks. Wendell is CCIE 1624, is a Certified Cisco Systems...
The network Command
Each network command enables RIP or IGRP on a set of interfaces. However, as a CCNA, you must understand the subtleties to what that really means (as explained in the next several paragraphs.) However, what enables really means in this case is not obvious from Cisco IOS documentation. Also, the parameters for the network command are not intuitive to many people new to Cisco IOS configuration commands therefore, routing protocol configuration, including the network command, is a likely topic for...
Data Link Function 1 Arbitration
Arbitration is needed only when there are instants in time during which it is not appropriate to send data across the media. LANs were originally defined as a shared media on which each device must wait until the appropriate time to send data. The specifications for these data link protocols define how to arbitrate the use of the physical medium. Ethernet uses the carrier sense multiple access collision detect (CSMA CD) algorithm for arbitration. The basic algorithm for using an Ethernet when...
Time Exceeded ICMP Message
The CCNA exam requires that you understand how routing protocols avoid creating routing loops. However, if a loop occurs, the Time To Live (TTL) field in the IP header is used to time out looping packets so that the packets do not loop forever. The Time Exceeded ICMP message is used in conjunction with the IP TTL header field. One of the two codes for Time Exceeded will be described here namely, the Time To Live (TTL) code option. An analogy for Time Exceeded may help. In the 1970s, a science...
Using Secondary Addresses
As a CCNA, Cisco expects you to be comfortable and familiar with IP address planning issues. One such issue involves what to do when there are no more unassigned IP addresses in a subnet. One alternative solution is to change the mask used on that subnet, making the existing subnet larger. However, changing the mask could cause an overlap. For example, if 10.1.4.0 24 is running out of addresses and you make a change to mask 255.255.254.0 (9 host bits, 23 network subnet bits), an overlap can...
OSI Layers
The OSI model consists of seven layers, each of which can (and typically does) have several sublayers. Cisco requires that CCNAs demonstrate an understanding of each layer as well as the protocols that correspond to each OSI layer. The names of the OSI model layers and their main functions are simply good things to memorize. And frankly, if you want to pursue your Cisco certifications beyond CCNA, these names and functional areas will come up continually. The upper layers of the OSI model...
Standard IP Access Lists
Standard access lists can match only by examining the source IP address field in the packet's IP header. Any bit positions in the 32-bit source IP address can be compared to the access list statements for example, a subnet number can be checked. However, the matching is flexible and does not consider the subnet mask in use it is just a math problem A wildcard mask defines the subset of the 32 bits in the IP address that must be matched. As a CCNA, you will be required to fully understand the...
D n
Example 5-2 Albuquerque Router Configuration and EXEC Commands enable secret 5 1 skrN z4oq6OHfB6zu1WG4P 6ZY0 interface Serial0 ip address 10.1.128.251 255.255.255.0 interface Serial1 ip address 10.1.130.251 255.255.255.0 Example 5-2 Albuquerque Router Configuration and EXEC Commands (Continued) n interface Ethernet0 ip address 10.1.1.251 255.255.255.0 Should've taken a left turn here This is Albuquerque C line con 0 password cisco login line aux 0 line vty 0 4 password cisco login Codes C -...
Exams Required for Certification
To certify for CCNA, a single exam is required Sylvan Prometric exam number 640-507. For CCDA, a single exam is required as well, but multiple exams are required for CCNP and CCDP. The exams generally match the same topics that are covered in one of the official Cisco courses, but in most cases and certainly on the CCNA exam more topics are covered on the exam than are in the course. Table 1-1 outlines the exams and the courses with which they are most closely matched. Course Most Closely...
Extended IP Access Lists
Extended IP access lists are almost identical to standard IP access lists in their use. The key difference between the two types is the variety of fields in the packet that can be compared for matching by extended access lists. To pass the CCNA exam, you must remember all the items that an extended IP access list can check to make a match. As with standard lists, extended access lists are enabled for packets entering or exiting an interface. The list is searched sequentially the first statement...
Command Line Interface
Cisco uses the acronym CLI to refer to the terminal user command-line interface to the IOS. The term CLI implies that the user is typing commands at a terminal, terminal emulator, or Telnet connection. Although you can pass the CCNA exam without ever having used the CLI, actually using the CLI will greatly enhance your chances. To access the CLI, use one of three methods, as illustrated in Figure 2-3. Figure 2-3 CLI Access Regardless of which access method is used, a CLI user initially is...
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. This 12-question quiz helps you determine how to spend your limited study time. The quiz is sectioned into three smaller four-question quizlets, which correspond to the three major topic headings in the chapter. Figure 2-1 outlines suggestions on how to spend your time in this chapter...
Troubleshooting Routing and Routing Protocols
It is no secret that Cisco would very much like all its certification exams CCNA included to be exams that prove that the test taker can build and troubleshoot live networks. Some people work with Cisco routers daily. Others' current job function does not allow frequent access to routers if this applies to you, you likely are trying to pass this certification so that you can move into jobs that involve routers and switches. The show ip route command has a myriad of options that will be helpful...
Data Encapsulation
The concept of placing data behind headers (and before trailers) for each layer is typically called encapsulation by Cisco documentation. As seen previously in Figure 3-2, when each layer creates its header, it places the data given to it by the next-higher layer behind its own header, thereby encapsulating the higher layer's data. In the case of a data link (Layer 2) protocol, the Layer 3 header and data are placed between the Layer 2 header and the Layer 2 trailer. The physical layer does not...
Navigating the Ios Cli
Several references are available for help when you are using the IOS. IOS documentation is available on CD and is free from Cisco if you own one router or switch under a current maintenance agreement. Paper documentation is also available from Cisco. If you prefer, Cisco Press offers the Cisco Documentation series (more information at www.ciscopress.com). In addition, all Cisco documentation is available online at Cisco's Web site (www.cisco.com univercd home home.htm) the IOS command reference...
Binary View of Subnetting
The benefit of a binary definition of subnetting is that it is exact. For a full understanding of subnetting particularly more advanced subnetting topics as well as other IP addressing and routing topics beyond the scope of this book, an exact definition is required. If your job will include planning subnet number assignment or troubleshooting, this binary understanding will be useful. Ray 150.150.1.0 150.15a2.0 Vinnie Ray 150.150.1.0 150.15a2.0 Vinnie A review of some basic concepts relating...
LAN Switching
An Ethernet switch appears to use the same logic as a transparent bridge. However, the internal logic of the switch is optimized for performing the basic function of choosing when to forward and when to filter a frame. Just as with a transparent bridge, the basic logic of a LAN switch is as follows Step 2 If the destination is a broadcast or multicast, forward on all ports. Step 3 If the destination is a unicast and the address is not in the address table, forward on all ports. Step 4 If the...
Cisco CCNA Exam 640507 Certification Guide
Cisco CCNA Exam 640-507 Certification Guide Copyright 2000 Lacidar Unlimited, Inc. Cisco Press logo is a trademark of Cisco Systems, Inc. All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America...
Choosing Which IOS Image to Load
The CCNA exam requires you to be proficient in configuring a router to load an IOS image from many sources. Two methods are used by a router to determine where it tries to obtain an IOS image to execute. The first is based on the value of the configuration register, which is a 16-bit software register in Cisco's more recently developed routers. (Some older routers had a hardware configuration register, with jumpers on the processor card, to set bits to a value of 0 or 1.) The second method used...
Connection Oriented Versus Connectionless Protocols
The terms connection-oriented and connectionless have some relatively well-known connotations inside the world of networking protocols. However, the typical connotation can be a bit misleading. For instance, most people correlate connection-oriented protocols with reliable or error-recovering protocols because the two features are often implemented by a single protocol. However, connection-oriented protocols do not have to provide error recovery, and error-recovering protocols do not have to be...
Qa
As mentioned in Chapter 1, All About the Cisco Certified Network Associate Certification, the questions and scenarios in this book are more difficult than what you should experience on the actual exam. The questions do not attempt to cover more breadth or depth than the exam however, they are designed to make sure that you know the answer. Rather than allowing you to derive the answer from clues hidden inside the question itself, the questions challenge your understanding and recall of the...
LAN Switch Configuration
Cisco expects CCNAs to master the concepts behind LAN switching and VLANs. This mastery includes the ability to configure IOS-based LAN switches using the IOS CLI. This section outlines the similarities of the switch IOS CLI to the router IOS CLI, as well as contrasting the commands, syntax, and required configuration elements unique to switches. Not all Cisco LAN switches provide an IOS CLI interface to the network engineer. Cisco wants its certifications to prove that the candidate knows the...
Recommended Training Path for CCNA
Cisco recommends that you take two courses before you take the CCNA exam. The first, Internetworking Technology Multimedia (ITM), is a CD-based course that you can order directly from Cisco currently for 50. This course covers many of the protocol basics needed for CCNA. The other suggested course is the instructor-led Interconnecting Cisco Network Devices (ICND) course, which is available from almost every Cisco training partner (for a list of training partners, go to The ICND course replaces...
