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...

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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...

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...

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 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...

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...

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 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 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...

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...

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...

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...

Resolving Problems at the Network Layer

You learned in Chapter 9, Isolating a Problem at the Network Layer, that common and possible symptoms of network layer problems include the following On the failing link, no component appears to be functional above the network layer. The network is operating, but it is operating either consistently or intermittently below the baseline level. The transport layer cannot transfer data or achieve connectivity. Routing tables are empty, inconsistent, or incomplete. Routing behavior is unexpected....

Resolving Problems at the Transport and Application Layers

Chapter 11, Isolating a Problem at the Transport or Application Layer, presented a set of common symptoms for each of the transport and application layer-related problems. Table 13-2 provides a summary of those symptoms for your review. Table 13-2 Common Symptoms of Transport and Application Layer Problems Table 13-2 Common Symptoms of Transport and Application Layer Problems Common Symptoms of Problems Occurring at the Transport Layer Common Symptoms of Problems Occurring at the Application...

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 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 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 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 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

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

Vlan Trunks

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...

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

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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,...