Acknowledgments

I did not have the pleasure of getting to know or communicating with all the individuals who have put their valuable time and effort into this book, but I would like to take this opportunity to sincerely thank each and every one of them. Among those with whom I worked directly were Brett Bartow (executive editor) and Andrew Cupp (development editor). These gentlemen are always a pleasure to work with, and I thank them for their patience, professionalism, and understanding. I would also like to...

Cisco Commands Used to Correct Problems Occurring at the Network Layer

This section lists a collection of Cisco IOS commands. These commands are used to correct different types of network layer problems and can be categorized as follows A brief explanation is provided for each Cisco IOS command. The following command enables or disables (with the no form of the command) the ability of the router to generate a request for name to IP address resolution. If you are using the ip name-server ip-address global configuration command, an address for the name server is...

Clock rate 64000

Which Cisco IOS command allows you to test connectivity to an IP host or device ping destination 5. Name the Cisco IOS command that allows you to set the encapsulation type on a router interface. Specify the mode in which the command must be entered. The command that allows you to set the encapsulation type on a router interface is encapsulation, and you must enter it from within interface configuration mode. 6. Which command allows you to change the Frame Relay LMI type on an interface The...

Command Syntax Conventions

The conventions used to present command syntax in this book are the same conventions used in the IOS Command Reference. The Command Reference describes these conventions as follows Vertical bars ( ) separate alternative, mutually exclusive elements. Square brackets indicate optional elements. Braces indicate a required choice. Braces within brackets indicate a required choice within an optional element. Boldface indicates commands and keywords that are entered literally as shown. In actual...

Commands and Applications Used to Gather Information About End System Network Configurations

You use many commands and applications to gather information or to perform diagnosis on end systems (IP hosts). An operating system might support some commands similar to other operating systems and might support some unique commands or applications. Table 2-5 lists some general commands offered on most operating systems. Table 2-5 General End System Network Configuration Information Gathering Commands Table 2-5 General End System Network Configuration Information Gathering Commands Sends an...

Commands and Applications Used to Isolate Problems Occurring at the Application Layer

This section presents a set of commands that you can use to isolate problems at the application layer. First, it introduces a set of commands used on end systems. Next, it discusses a set of Cisco IOS commands that display information related to host table, e-mail (Post Office Protocol 3 POP3 , SMTP, Internet Message Access Protocol IMAP ), network management (Simple Network Management Protocol SNMP , NTP), file management (FTP, TFTP), Telnet, and DHCP. The ifconfig -a command is a useful...

Comparing Layered Networking Models

This section explains the 4-layer TCP IP model by comparing it to the OSI model and by describing the function of each of its layers. Figure 3-2 displays the 7-layer OSI model and the 4-layer TCP IP model side by side. As displayed, similar to the OSI networking model, the TCP IP networking model divides networking architecture into modular layers. Figure 3-2 shows how the TCP IP networking model maps to the layers of the OSI networking model. Figure 3-2 Comparing the OSI Model with the TCP IP...

Components of a Network Configuration Table

Network configuration tables store accurate information about the hardware and software components of a network. Recording data into these tables, referring to these tables to look up information, and maintaining the accuracy of these tables are easier and more pleasant than using documentation that is composed of massive amounts of text and configuration printouts. Network configuration tables should hold essential information about the network devices and not be cluttered with unimportant...

Components of a Topology Diagram

The network topology diagram is the second piece of documentation (after the network configuration table), and it is considered an essential part of any network baseline. This diagram is a graphical representation of the network that must illustrate all the devices and how they are connected. Physical and logical detail about the network are revealed using consistent notations and symbols. Figure 1-1 is an example of a network topology diagram. In Figure 1-1, you can see a network cloud symbol...

Components of an End System Network Configuration Table

The purpose of this section is to identify the information that you should record in an end system network configuration table used to troubleshoot end systems. The network configuration table, as baseline documentation, should hold accurate and up-to-date information about the software and hardware used in end systems. The following is a list of items to record in an end system network configuration table Device name and its role or function (purpose), if any Default gateway, DNS server, and...

Components of an End System Network Topology Diagram

The end system network topology diagram has its focus on the end systems it graphically depicts. It illustrates how end systems are both physically and logically connected to the network. An end system network topology diagram is a graphical presentation of its counterpart end system network configuration table. Nonetheless, it is not practical for a network topology diagram to include every component of the end system network configuration table. Therefore, vital and essential information such...

Contents

Introduction xvi Part I Establishing a Baseline 3 Chapter 1 Creating Network Configuration Documentation 5 Do I Know This Already Quiz 5 Foundation Topics 11 Components of a Network Configuration Table 11 Components of a Topology Diagram 14 Discovering Network Configuration Information 16 The Process of Creating Network Documentation 18 Guidelines for Creating Network Documentation 19 Foundation Summary 21 Q& A 25 Chapter 2 Creating End System Network Configuration Documentation 27 Do I Know...

Correcting a Physical or Data Link Layer Problem

The following are suggested steps for correcting an isolated problem at the physical and data link 1. Ensure that you have a valid saved configuration for any device on which you intend to modify the configuration. This provides for eventual recovery to a known initial state. 2. Make initial hardware and software configuration changes. If the correction requires more than one change, make only one change at a time. 3. Evaluate and document the changes and the results of each change that you...

Correcting a Problem at the Transport or Application Layer

This chapter focuses on correcting the problems that you have already isolated using the commands and guidelines presented in Chapter 11, Isolating a Problem at the Transport or Application Layer. The first section presents useful commands for correcting problems categorized as transport layer problems, and the second section provides the commands for correcting problems associated with the application layer. Next, this chapter lists the support resources available to network support personnel...

Correcting Problems Occurring at the Network Layer

This section provides a step-by-step procedure that you can use to correct isolated problems at the 1. Ensure that you have a valid saved configuration for the device whose configuration you intend to modify. This provides for eventual recovery to a known initial state. 2. Make initial hardware and software configuration changes. If the correction requires more than one change, make only one change at a time. 3. Evaluate and document the changes and the results of each change that you make. If...

Creating Network Configuration Documentation

The elements of a network can be classified into two groups Networking devices, such as routers and switches End systems, such as servers and workstations The network baseline must include information on both of these groups. The network baseline and network configuration documentation can serve as a troubleshooting tool to diagnose a problem and, more importantly, to correct it. The network baseline information (about network devices) is recorded in network configuration tables and topology...

Dedication

I would like to dedicate this book to those whose lives have a positive impact on the lives of others. I wish that people would live and take actions based on their beliefs, rather than merely have beliefs and take no actions. I thank my parents and sisters my wife, Elke my children and the rest of my invaluable family and friends for making my life better. I am confident that my children, Thalia, Ariana, and Armando, will have a life full of health, prosperity, and happiness however, my hope...

Discovering End System Network Configuration Information

This section presents an 8-step method for discovering network configuration information of end systems. Each step is about discovering a specific piece of information and requires executing a special action or command. These steps along with their descriptions and their corresponding actions and commands are organized and presented in Table 2-8. Table 2-8 Discovering End System Network Configurations Table 2-8 Discovering End System Network Configurations Discover and view information about...

Do I Know This Already Quiz

The purpose of the Do I Know This Already quiz is to help you decide if you really need to read this entire chapter. If you already intend to read the entire chapter, you do not 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 determine how to spend your limited study time. Table 1-1 outlines the major topics discussed in this chapter and the Do I Know This Already quiz questions that correspond...

Dshow controllers

Which of the following is not a fit guideline for isolating problems at the physical and data link layers a. Check operational status and data error rates of the interfaces and check proper interface configurations. c. Check for bad cables or connections. You can find the answers to the Do I Know This Already quiz in Appendix A, Answers to the 'Do I Know This Already ' Quizzes and 'Q& A' Sections. The suggested choices for your next step are as follows 8 or less overall score Read the...

Dshow ip interface brief

You have been informed that a group of users lost its connection to the network due to a problem in either the physical or data link layer. You check the operational status, errors, and configuration of the affected interfaces. You still have not found the cause of the problem. Which guideline for isolating a problem at the physical and data link layers have you omitted a. Verifying the IP address of the default gateway b. Checking cable configuration d. Viewing TCP information on a host 5....

End System Commands and Applications Used to Isolate Problems Occurring at the Network Layer

Table 9-2 describes some general end system commands, some commands specific to Microsoft Windows operating systems, and some UNIX Mac OS X commands that you can use to isolate problems at the network layer. Although many such commands also display information that concerns the data link layer, they are noteworthy at the network layer because they highlight problems in the interface between the data link and network layers. Table 9-2 End System Commands to Isolate Network Layer Problems Table...

Examples That Demonstrate Correction of Network Layer Problems

So that you can practice correcting a network layer problem that has already been isolated, this section continues and corrects the two cases that were started in the previous chapter. To refresh your memory, both cases begin with the background information. Correcting an Access List to Stop a Router from Rejecting a Prefix Sent from a BGP Peer You are the second-level network engineer responsible for sites in Washington, Baltimore, and Columbia. (The routers in each city are named after the...

Foundation Topics

Gathering a comprehensive collection of symptoms allows you to understand and recognize the problem and be able to describe and document it. Misunderstanding or having an incomplete perception of the problem can waste valuable time and resources on factors that might not be relevant to the problem. The time it takes you to collect a comprehensive set of symptoms is well worth it because it helps focus your efforts on the problem at hand. Therefore, it is essential that if you are planning to...

Gathering Symptoms

Chapter 5, Gathering Symptoms, presents a flow diagram (see Figure 13-1) that depicts the process of gathering symptoms from a network. Figure 13-1 Gathering Network Symptoms Figure 13-1 Gathering Network Symptoms The process of gathering symptoms from a network is composed of the following steps 1. Analyze Existing Symptoms After you gather symptoms from the users, end systems, or trouble ticket documents, you must analyze the symptoms and describe the problem. 2. Determine Ownership Based on...

Gathering User Symptoms

This section provides a set of guidelines for gathering symptoms from users, a set of general questions to ask the users during the Gathering Symptoms process, and an example of how to follow the guidelines and put the general questions to use. The following list presents the guidelines for gathering symptoms for a user's hardware or software Ask questions that are pertinent to the problem. Use each question as a means to either eliminate or discover possible problems. Speak at a technical...

Guidelines for Creating Network Documentation

To produce effective, efficient, and easy-to-use network documentation, you should determine the documentation's scope, know its objective, be consistent, make it available yet secure, and keep it up to date by properly maintaining it. These points are listed and briefly explained in Table 1-7. Table 1-7 Guidelines for Creating Network Documentation Table 1-7 Guidelines for Creating Network Documentation Know which devices are part of your domain of responsibility. Collect data that is relevant...

Guidelines for Isolating a Problem Occurring at the Transport or Application Layer

The following guidelines help to isolate problems that are rooted at the transport and application Establish that the problem is not at the network or lower layers by testing and proving IP connectivity between two points of interest. If you are troubleshooting e-mail-related problems, beware of the fact that sending and receiving e-mail utilize and depend on different protocols and might involve multiple components therefore, you must test those functions separately. You might have to research...

Identifying Commands and Applications Used to Correct Problems Occurring at the Transport Layer

Network administrators and engineers occasionally use access lists, sometimes called access control lists (ACLs), to perform different types of tasks. One such task is controlling what packets can enter and which packets can exit particular router interfaces. You create an ACL in global configuration mode. If you apply the ACL to an interface from within interface configuration mode, it can control what packets can get in or out of that interface depending on whether it is applied in the in or...

Identifying the Symptoms of Problems Occurring at the Data Link Layer

When the data received from or sent to the network layer is not properly encapsulated into or de-encapsulated from data link layer frames, or when data link layer frames are not properly formed, transmitted, and received across working physical layer links, you have data link layer problem(s). Improper frame types (mismatched encapsulations), duplicate MAC addresses, and misbehaving Layer 2 devices such as switches or bridges (due to various configuration or hardware problems or limitations...

Identifying the Symptoms of Problems Occurring at the Physical Layer

Because the components of the OSI model's physical layer are tangible and can be inspected physically, this layer is somewhat unique relative to the other layers. Examples of the physical layer components include interfaces ports, modules, cables, connectors, adapters, transceivers, and so on. Problems at the physical layer might cause complete or intermittent loss of data across a link, generating symptoms such as application failures or data transfers at lower than expected rates. If you log...

Identifying Transport and Application Layer Support Resources

This section identifies some valuable support resources that are at your disposal. Cisco Connection Online (CCO), which is Cisco's official Web site, and Cisco's documentation pages offer a tremendous amount of useful information (see Figure 12-1). The Internet Engineering Task Force (IETF), International Telecommunications Union (ITU), Frame Relay Forum (FRF), and ATM Forum also provide valuable information on their Web pages. Figure 12-1 Cisco Connection Online (CCO) and Documentation Figure...

Isolating a Problem at the Network Layer

This chapter first discusses and identifies the symptoms of problems that occur at the network layer. As you will see, with physical and data link layers in good working condition, erroneous addressing or routing configurations cause most network layer problems. Next, this chapter presents the end system commands and applications that are used to isolate network layer problems. You analyze the output of those commands and applications to isolate the problems occurring at this layer. Finally,...

Isolating a Problem at the Transport or Application Layer

To isolate problems at the transport and application layers, you use the general troubleshooting process for analyzing the gathered symptoms. The troubleshooting approach at these layers is similar to the processes presented in the previous chapters for the lower OSI layers. At the transport and application layers, issues usually revolve around whether the application is running at the target device, whether name resolution operates with success, whether router access lists permit flow of...

Isolating a Problem Occurring at the Network Layer

The guidelines for isolating problems at the network layer are presented here. The goal of the following guidelines is to equip you with a set of effective and systematic techniques that elevate the chance of swift and successful network layer problem isolation Identify a single pair of problematic source and destination devices When you have identified the two devices that are the most likely source of the connectivity problem, test the connectivity between the two devices. Ping a device...

Network Documentation

In Chapter 1, Creating Network Configuration Documentation, you learned that to create effective network documentation, you must do the following Determine the scope of your work You must find out what part of the network you are responsible for and which devices you need to include in your work. Know your objective Collect and document information about the elements within your scope. While making certain that you provide sufficient detail, you must also avoid collecting and documenting too...

Network Layer Support Resources

Despite the level of your knowledge and experience about networking protocols, tools, and commands, sometimes you will need to consult an outside resource. These support resources are commonly used as reference materials for commands and configuration procedures, as well as research for technology-specific information and industry standards. Given the ability to use online support resources for effective research, you save yourself time that you might have otherwise spent on the phone with a...

No

Named access lists, 221 NBT (NetBIOS over TCP), 202 netstat command, 155, 201 collecting information, 16-18 creating, 18-20 end system network configuration tables, 31 collecting data, 35-36 creating, 38 discovering configuration information, 37-38 network diagrams, 165 network layer (OSI model), 54 common symptoms of problems, 153 correcting problems, 246-250 end system commands, 179 interface configuration commands, 175-177 IP access list commands, 177 IP routing commands, 178 resources, 186...

Objective of This Book

During the time that I was preparing this book, I kept my focus on only one goal preparing the readers for the 642-831 CIT exam. Throughout the book, I present what I think is absolutely essential for you to know before you attempt the new CCNP CIT exam. The content is similar to that of the CIT course, but the large volume of exam-oriented tools such as the summary tables, figures, questions and answers, and, of course, the accompanying CD make this book ideal for exam preparation. My...

Establishing a Baseline

One of the goals of network support professionals and engineers is to eliminate or at least minimize the down time of a network. Having a complete and up-to-date network baseline helps accomplish that goal. The network baseline can be defined as a snapshot of the configuration of a network while it is operating under normal conditions. During troubleshooting or disaster recovery, the baseline is used as a guide to return the network to its normal condition efficiently. Without guesswork and...

Determining an Effective Troubleshooting Strategy

An organization needs an effective troubleshooting strategy. An effective troubleshooting strategy facilitates discovery of the source of the problem, isolating the problem area, and solving the problem. This process needs to be time and cost sensitive otherwise, business opportunities are lost and user confidence in the organization's competence is reduced. Chapters 3-6 cover different aspects and topics related to effective troubleshooting strategy. Chapter 3 emphasizes understanding of the...

Resolving Problems at the Network Layer

Because the processes and methods of gathering symptoms, isolating problems, and correcting problems at the physical and data link layers have been dealt with, Part IV moves on to accomplishing the same tasks at the network layer. The goal of Chapters 9 and 10 is to show you how to perform the isolation and correction phases of the general troubleshooting process to resolve failure and optimization problems at the network layer of the OSI model. As you will notice, the symptoms of the problem,...

Resolving Problems at the Transport and Application Layers

The process for isolating and correcting problems at the transport and application layers is the same as the process of isolating and correcting problems at the lower layers. However, at the transport and application layers, the symptoms that the problems present, as well as the commands, applications, and steps used to successfully resolve them, are different. Part V discusses the isolation and correction phases of the general troubleshooting process to resolve failure and optimization...

Scenarios

Chapter 13 CIT Scenarios and Examples This chapter includes scenarios and examples that cover topics from throughout this book. These scenarios and examples will help solidify your mastery of the CIT topics. The following topics are covered in the scenarios and examples in this chapter Resolving problems at the physical or data link layer Resolving problems at the network layer Resolving problems at the transport and application layers

Appendix

Appendix A contains the answers and explanations to the chapter quizzes. Do I Know This Already Quizzes Each chapter begins with a quiz that helps you determine the amount of time you need to spend studying that chapter. If you follow the directions at the beginning of the chapter, the Do I Know This Already quiz directs you to study all or particular parts of the chapter. Foundation Topics These are the core sections of each chapter. They explain the protocols, concepts, and configuration for...

Physical and Data Link Layer Support Resources

During the course of troubleshooting, you can run out of ideas and essentially feel stuck at a dead end. Many resources are available. In addition to colleagues, certified Cisco consultants and Cisco Technical Assistance Center personnel are valuable resources. Cisco Connection Online (CCO) has information on various legacy and new technologies, configuration and troubleshooting of Cisco devices, design and migration solutions, and so on. The following is a list of online resources that Cisco...

Qa

As mentioned in the introduction, you have two choices for review questions. The questions that follow give you a bigger challenge than the exam because they use an open-ended question format. By reviewing now with this more difficult question format, you can exercise your memory better and prove your conceptual and factual knowledge of this chapter. You can find the answers to these questions in Appendix A. For more practice with exam-like question formats, including questions that use a...

Selecting a Troubleshooting Approach

Selecting the most effective troubleshooting approach to solve a network problem allows you to resolve the problem in a quicker, more cost-effective manner. To select an effective troubleshooting approach, you must do the following 1. Determine the scope of the problem. Determining the scope of the problem means selecting the troubleshooting approach based on the perceived complexity of the problem. A bottom-up approach typically works better for complex problems. A top-down approach is...

Show ip bgp summary show ip bgp neighbors

Which Cisco IOS command displays the content of the BGP table show ip bgp 10. It is important to use an effective and systematic technique to successfully isolate a problem at the network layer. Provide at least two of the recommended guidelines for isolating network layer problems. Following are the recommended guidelines for isolating network layer problems Identify a single pair of problematic source and destination devices. Ping a device across the connection. Test connectivity at each hop...

Show ip eigrp neighbors

List at least three commands that are useful for discovering network configurations on standard switches. The following commands are useful for discovering network configurations on standard 6. List the five stages of the process of creating network documentation. Following are the five stages in the process of creating network documentation Stage 2 Interface Discovery 7. What are the rules guidelines for creating network documentation The following are the rules guidelines for creating network...

Step 1 Step 2 Step

View information about the operating system and hardware of the device Windows System icon in the Control Panel Mac OS About This Mac from Apple icon Access a command line Windows MS-DOS or Command Prompt Mac OS Utilities folder in Applications directory View detailed information about the TCP IP settings of the device Windows ipconfig all or winipcfg UNIX or Mac OS ifconfig -a UNIX or Mac OS route -n Step 5 View ARP information

Symptoms of Problems Occurring at the Application Layer

The application layer of the TCP IP suite maps to the session (Layer 5), presentation (Layer 6), and application (Layer 7) layers of the OSI model. Therefore, issues that are related to any of these layers should be referred to as application layer problems within the TCP IP framework. You can categorize a problem as a pure application layer problem if you can prove that all the lower layers up to the transport layer are in good working condition. Application layer problems might be rooted at...

Symptoms of Problems Occurring at the Transport Layer

When the transport layer has problems, you can observe the symptoms at the application layer. Session layer protocols and network applications rely on the correct operation and services that the transport layer provides. With transport layer problems, users notice a lack of connectivity to network resources or network applications that do not function. The main transport layer protocols of the TCP IP suite are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). (Real-Time...

The BottomUp Troubleshooting Approach

The bottom-up approach to troubleshooting a networking problem starts with the physical components of the network and works its way up the layers of the OSI model. If you conclude that all the elements associated to a particular layer are in good working condition, you inspect the elements associated with the next layer up until the cause(s) of the problem is are identified. Figure 6-1 shows the bottom-up troubleshooting approach. Figure 6-1 A Bottom-Up Troubleshooting Approach Figure 6-1 A...

The Correct the Problem Stage

After you have an isolated problem at hand, you must propose the corresponding corrective action(s). If the actions are multiple and independent (atomic), implement them one at a time. Making few or one change at a time allows for more granular and discrete observation and evaluation of their results moreover, one or a few actions are easier to roll back if necessary. Therefore, note that not all changes stick you might have to withdraw some. Furthermore, keep in mind that one or few changes...

The Divideand Conquer Troubleshooting Approach

The divide-and-conquer approach to network troubleshooting, unlike its top-down and bottom-up counterparts, does not always commence its investigation at a particular OSI layer. When you apply the divide-and-conquer approach, you select a layer and test its health based on the observed results, you might go in either direction (up or down) from the starting layer. Figure 6-3 depicts the divide-and-conquer troubleshooting approach. If a layer is in good working condition, you inspect the layer...

The Gather Symptoms Stage

During the Gather Symptoms stage of the general troubleshooting process, you gather and document symptoms from the network, end systems, or users. The process is usually initiated when someone reports a problem verbally, via e-mail or voice mail, or through another form of problem reporting. Subsequently, you must try to define the problem. Defining the problem usually involves interviewing users, seeing the problem first hand, and talking to peers, support staff, and engineers. The symptoms...

The General Troubleshooting Process

Solving network problems effectively and in a timely manner requires following a systematic troubleshooting methodology. The goal of this chapter is to present a general process and methodology that you can use in any network troubleshooting situation. The benefit of applying this general process is that it helps you systematically resolve problems quicker and more cost effectively, with less confusion and wasted time. To appreciate the importance of using a systematic troubleshooting method,...

The Isolate the Problem Stage

Isolating the problem starts when, based on the gathered symptoms, initial interviews, and so on, some of the initial possibilities are ruled out, and the others remain as probable culprits. However, the remaining possibilities must be ranked based on their likelihood, and their validity should be evaluated individually. The way that the possibilities are tested, reinstated, or overthrown is based on the tests conducted and the fact-gathering methods that were employed. Gathering symptoms is...

The Layers of a Logical Model

This section identifies the logical layers that you should focus on when troubleshooting specific networking devices. The ability to identify which layers of the logical networking model pertain to a networking device allows a troubleshooter to minimize the complexity of a problem by dividing the problem into manageable parts. Table 3-2 shows what logical layers the different internetworking devices map to. The ability to map networking devices to logical network layers can focus...

The Organization and Features of This Book

Because the new CIT examination closely reflects the material presented in the Cisco official CIT training material, I made a point of making sure the flow of this book matches that of the CIT's official training curriculum. This book is also accompanied by a CD-ROM that offers multiple-choice questions out of the entire book's content. The simulated exam and study tools are specifically designed to complement the material in this book, provide a thorough study medium, and prepare you for the...

The Process of Creating Network Documentation

To create network documentation, you must log into each device, one at a time, and discover and document its network configurations. You can hop from one device to its undocumented neighbor(s) and repeat this process until you are finished. Figure 1-2 depicts the stage-by-stage process of creating network documentation by using a flow chart. Table 1-6 provides an explanation for each of the stages shown in Figure 1-2. Figure 1-2 Creating Network Documentation Figure 1-2 Creating Network...

The Symptoms of Problems Occurring at the Network Layer

When the network layer or higher experiences symptoms or difficulties, it might be difficult to determine exactly at which layer the root problem is located. The reason is that the symptom or problem might also have sprung from physical or data link layer failures. If troubleshooting efforts show that the physical and data link layers are problem free, then you have a concrete indication that your problem resides at the network layer or higher. Following are some common symptoms of network...

The Top Down Troubleshooting Approach

As its name implies, when you apply a top-down approach to troubleshooting a networking problem, you start with the user application and work your way down the layers of the OSI model. Figure 6-2 shows the top-down troubleshooting approach. If a layer is not in good working condition, you inspect the layer below it. When you know that the current layer is not in working condition and you discover that a lower layer works, you can conclude that the problem is within the layer above the lower...

This chapter covers the following subjects

Symptoms of problems occurring at the transport layer Symptoms of problems occurring at the application layer Commands and applications used to isolate problems occurring at the transport layer Commands and applications used to isolate problems occurring at the application layer Guidelines for isolating a problem occurring at the transport or application layer

[no debug

The following list presents the guidelines for gathering symptoms for a user's hardware or software Ask questions that are pertinent to the problem. Use each question as a means to either eliminate or discover possible problems. Speak at a technical level that a user can understand. Ask the user when he first noticed the problem. If possible, ask the user to re-create the problem. Determine the sequence of events that took place before the problem occurred. Match the symptoms that the user...

Creating End System Network Configuration Documentation

The purpose of this section is to provide guidelines on creating good end system network configuration documentation. Good documentation provides up-to-date, sufficient, and accurate information about the end systems' network configuration. The guidelines are listed and explained in Table 2-9. Creating End System Network Configuration Documentation 39 Table 2-9 Guidelines for Creating End System Network Configuration Documentation Table 2-9 Guidelines for Creating End System Network...

Commands and Applications Used to Isolate Problems Occurring at the Transport Layer

To ascertain that a problem is rooted at the transport layer rather than at a layer below it, you must use proper tools and commands. You can test the operability of Layers 1, 2, and 3 by using the Windows commands ping, tracert, netstat, and nbtstat. If the results prove that the lower layers (physical, data link, and network) are in good working order, you can focus your attention on Layer 4-related issues such as filters, policies, quality of service (QoS) tools, and so on. You can use the...

About the Technical Reviewers

Craig Dorry, CCIE No. 9072, is a network architect and Tier 3 network support engineer for AT& T Solutions, where he is the escalation contact for high-profile and business-impacting network issues. Craig has more than eight years of experience in network implementation and support at the LAN and WAN level. He has strong knowledge of routing protocol performance issues as well as network diagnostic and management equipment. Don Johnston is a certified Cisco Systems instructor and consultant...

Cisco Press

800 East 96th Street, 3rd Floor Indianapolis, Indiana 46240 USA CCNP CIT Exam Certification Guide Second Edition Amir S. Ranjbar, MSc., CCIE No. 8669 Copyright 2004 Cisco Systems, Inc. 800 East 96th Street, 3rd Floor Indianapolis, IN 46240 USA 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...

Resolving Problems at the Physical or Data Link Layer

Chapter 7, Isolating a Problem at the Physical or Data Link Layer, lists several common symptoms of problems occurring at the physical or data link layer. Table 13-1 provides a summary of those symptoms for your review. Table 13-1 Common Symptoms of Physical and Data Link Layer Problems Table 13-1 Common Symptoms of Physical and Data Link Layer Problems Common Symptoms of Problems Occurring at the Physical Layer Common Symptoms of Problems Occurring at the Data Link Layer No component above the...

Gathering Network Symptoms

Figure 5-1 displays the process of gathering symptoms from a network using a flowchart. Figure 5-1 sends the message that you must first ascertain that the problem is within your area of responsibility. Next, you must determine whether the symptoms and facts gathered are enough to identify the cause and take corrective actions. Sometimes gathering more facts is necessary when you have gathered enough information and determined the cause, you can take corrective actions. The stages of gathering...

Discovering Network Configuration Information

You must collect from each device the information that you need to record in network configuration tables and network topology diagrams by entering appropriate commands. In this section, two sets of commands for discovering network configuration information are presented. The first set is the commands to be used on routers and multilayer switches, and the second set is the commands to be used on standard switches. You should start the process of collecting the network configuration information...

Gathering End System Symptoms

This section presents a process you can use to gather symptoms from end systems. Figure 5-2 displays this process with a flowchart. The process starts with interviewing the user and then calls for analyzing, determining, and documenting the symptoms. Finally, you correct the problem if it is possible. NOTE This book focuses on troubleshooting network connectivity. You might need to seek help from external vendors or workstation and server administrators to effectively troubleshoot problems at...

Analyzing Commands and Applications Used to Isolate Problems Occurring at the Physical and Data Link Layers

This section covers commands that you use to isolate problems at the physical and data link layers. This section also demonstrates isolating problems at physical and data link layers through some examples. Table 7-2 shows end system commands used to isolate problems at the physical and data link layers. The first part of this table lists general commands. The second section lists commands you enter at an end system running a version of the Windows operating system. In the third part of Table...

Correcting Problems Occurring at the Transport and Application Layers

This section details a brief yet beneficial procedure to be followed when correcting problems occurring at the transport and application layers (or in general). Because the order of execution is important, the steps are presented as a numbered list 1. Be sure that you have a saved configuration for the device whose configuration you are about to change. During the course of troubleshooting, you should always be able to revert back to a known initial state. Casually speaking, you want to make...

Identifying Commands and Applications Used to Correct Problems Occurring at the Application Layer

Service Timestamps Cisco

This section presents some commands that you can use to correct problems occurring at the application layer. The selected commands relate to SNMP, NTP, and Dynamic Host Configuration Protocol (DHCP). Of course, you can use other commands to configure and correct application layer problems. The Cisco Internetwork Troubleshooting (CIT) course intends to familiarize you with the troubleshooting process, rather than listing and explaining all Cisco IOS commands. This book also discusses those same...

The Encapsulated Data Flow Process

Lighting Truss Guy Wire

This section discusses the stages of data flow through a network that interconnects remote end systems and segments using Cisco routers and switches. This discussion includes the topic of encapsulation and decapsulation (or de-encapsulation), along with the different forwarding filtering performed by routers and switches. Figure 3-1 shows end system Host A and end system Host B communicating on a network. The encapsulated data flow process has four stages. In Figure 3-1, Stages 1 through 4...

Commands and Applications Used to Correct Problems Occurring at the Physical and Data Link Layers

The CIT course discusses certain commands with regards to correcting physical and data link problems. This section discusses those commands. Neither the CIT course nor this book imply by any means that you can fix all physical and data link layer problems by using these commands. The commands are listed and briefly described in Table 8-2. From there, a more detailed discussion of these controller and interface configuration commands is provided. The last part of this section gives examples on...

Foundation Summary

The Foundation Summary section of each chapter lists the most important facts from that chapter. Although this section does not list every fact from the chapter that will be on your CCNP exam, a well-prepared CCNP candidate should at a minimum know all the details in each Foundation Summary before taking the exam. Following are some common symptoms of network layer problems No component on the failing link appears to be functional above the network layer. The network is functional but is...

Analyzing Cisco Command and Application Output to Isolate Problems Occurring at the Network Layer

This section describes several important Cisco IOS commands that display information that is useful for isolating network layer problems (see Table 9-3). Following that, a scenario-style example demonstrates how you can use the commands listed in Table 9-3 to help isolate a realistic network layer problem. The first few commands listed in Table 9-3 are marked as general commands because they might reveal issues related to many aspects of configuration at the network layer (addressing, routing,...