ICND 2 Promo - Boson Frame Relay.....330 Understanding Frame Relay Topologies..... 331 Full-Mesh...

ICND2 Curriculum 640-816 Interconnecting Cisco Networking Devices Part 2 Version: Beta

Labs powered by

Interconnecting Cisco Networking Devices Part 2640-816 Curriculum

iv © 2012 Boson Software, LLC

The labs referenced in this book correspond to some of the labs available in the Boson NetSim 8 Network Simulator and have been printed in the Boson Lab Guide, which is available for purchase. To learn more about the Boson NetSim or to purchase and download the software, please visit www.boson.com/netsim-cisco-network-simulator.

Copyright © 2012 Boson Software, LLC. All rights reserved. Boson, Boson NetSim, Boson Network Simulator, and Boson Software are trademarks or registered trademarks of Boson Software, LLC. Catalyst, Cisco, and Cisco IOS are trademarks or registered trademarks of Cisco Systems, Inc. in the United States and certain other countries. Media elements, including images and clip art, are the property of Microsoft. All other trademarks and/or registered trademarks are the property of their respective owners. Any use of a third-party trademark does not constitute a challenge to said mark. Any use of a product name or company name herein does not imply any sponsorship of, recommendation of, endorsement of, or affiliation with Boson, its licensors, licensees, partners, affiliates, and/or publishers.

25 Century Blvd. Ste. 500Nashville, TN 37214

www.boson.com

v© 2012 Boson Software, LLC

ICND2 Table of Contents

Module 1: Troubleshooting Networks ...........................................................................................1

Overview .................................................................................................................................................... 2Objectives .................................................................................................................................................. 2Understanding the Systematic Approach .................................................................................................. 3Understanding Troubleshooting Techniques .............................................................................................. 5

Understanding the OSI Model ............................................................................................................. 5Implementing the OSI Techniques ...................................................................................................... 6

Understanding the Bottom Up Troubleshooting Technique ........................................................ 6Understanding the Top Down Troubleshooting Technique ......................................................... 6Understanding the Divide and Conquer Troubleshooting Technique ......................................... 7

Implementing the Non-OSI Techniques .............................................................................................. 8Understanding the Follow the Path Troubleshooting Technique ................................................ 8Understanding the Move the Problem Troubleshooting Technique ............................................ 8Understanding the Spot the Difference Troubleshooting Technique .......................................... 9

Understanding show Commands ............................................................................................................ 10Understanding debug Commands .......................................................................................................... 12Understanding the ping Command ......................................................................................................... 13Understanding the traceroute Command ............................................................................................... 14Review Question 1 ................................................................................................................................... 15Review Question 2 ....................................................................................................................................17Review Question 3 ................................................................................................................................... 19Lab Exercises .......................................................................................................................................... 21

Module 2: Implementing VLSMs and Summarization................................................................23

Overview .................................................................................................................................................. 24Objectives ................................................................................................................................................ 24Implementing VLSMs ............................................................................................................................... 25Understanding Subnets ........................................................................................................................... 26Understanding Subnetting ....................................................................................................................... 27Understanding VLSMs ............................................................................................................................. 28Implementing Route Summarization ........................................................................................................ 31

Understanding Discontiguous Subnets ............................................................................................. 32Understanding Routing Protocols ............................................................................................................ 33Configuring Classless Summarization ..................................................................................................... 34Choosing a Route .................................................................................................................................... 36Review Question 1 ................................................................................................................................... 38Review Question 2 ................................................................................................................................... 40Lab Exercises .......................................................................................................................................... 42

Module 3: Implementing ACLs .....................................................................................................43

Overview .................................................................................................................................................. 44Objectives ................................................................................................................................................ 44

vi © 2012 Boson Software, LLC


Understanding ACLs ................................................................................................................................ 45Understanding Wildcard Masks ............................................................................................................... 46Configuring Standard ACLs ..................................................................................................................... 47Configuring Extended ACLs .................................................................................................................... 50Understanding ACL Sequencing.............................................................................................................. 54Applying ACLs to an Interface ................................................................................................................. 57Verifying and Troubleshooting ACLs ........................................................................................................ 59Understanding Advanced ACLs ............................................................................................................... 60

Time-based ACLs .............................................................................................................................. 60Dynamic ACLs (lock and key) ............................................................................................................ 60Reflexive ACLs .................................................................................................................................. 61

Configuring ACLs to Control Router Access............................................................................................ 62Other Uses for ACLs ................................................................................................................................ 63Review Question 1 ................................................................................................................................... 64Review Question 2 ................................................................................................................................... 66Review Question 3 ................................................................................................................................... 68Lab Exercises .......................................................................................................................................... 70

Module 4: Implementing NAT and PAT ........................................................................................71

Overview .................................................................................................................................................. 72Objectives ................................................................................................................................................ 72Why Implement NAT? .............................................................................................................................. 73Understanding Inside Networks and Outside Networks ...........................................................................74Configuring NAT Interfaces...................................................................................................................... 75Understanding Local Addresses and Global Addresses ......................................................................... 76Understanding NAT Address Types ......................................................................................................... 77Understanding NAT Configuration Types ................................................................................................ 78

Understanding Static NAT ................................................................................................................. 79Configuring Static NAT ...................................................................................................................... 80Understanding Dynamic NAT ............................................................................................................ 81Configuring Dynamic NAT ................................................................................................................. 82Understanding PAT............................................................................................................................ 84Configuring PAT ................................................................................................................................ 85

Troubleshooting and Repairing NAT ........................................................................................................ 87Review Question 1 ................................................................................................................................... 89Review Question 2 .................................................................................................................................. 91Lab Exercises .......................................................................................................................................... 93

Module 5: Implementing IPv6 .......................................................................................................95

Overview .................................................................................................................................................. 96Objectives ................................................................................................................................................ 96Understanding the Differences Between IPv4 and IPv6 ......................................................................... 97Understanding IPv6 Address Composition .............................................................................................. 98

vii© 2012 Boson Software, LLC


Abbreviating IPv6 Addresses ............................................................................................................ 99Understanding IPv6 Address Prefixes ................................................................................................... 101Understanding IPv6 Address Types ...................................................................................................... 102Understanding Global Unicast Addresses and Route Aggregation ....................................................... 105Understanding IPv6 Address Configuration .......................................................................................... 107

Understanding EUI-64 Interface IDs ............................................................................................... 108Understanding Stateful and Stateless Address Configuration ........................................................ 109

Using IPv6 in an IPv4 World ...................................................................................................................110Dual Stack ........................................................................................................................................111NAT-PT .............................................................................................................................................112Tunneling ..........................................................................................................................................113

Routing IPv6 ...........................................................................................................................................114Review Question 1 ..................................................................................................................................115Review Question 2 ..................................................................................................................................117Review Question 3 ..................................................................................................................................119Lab Exercises .........................................................................................................................................121

Module 6: Implementing VLANs and Trunking ........................................................................123

Overview ................................................................................................................................................ 124Objectives .............................................................................................................................................. 124VLAN Overview ..................................................................................................................................... 125

What Do VLANs Do? ....................................................................................................................... 127IP Addressing Using VLANs .................................................................................................................. 128Creating and Configuring VLANs .......................................................................................................... 129Verifying VLANs..................................................................................................................................... 130Access Ports ...........................................................................................................................................131Configuring Access Ports ...................................................................................................................... 132Verifying VLAN Membership ................................................................................................................. 133Trunk Ports ............................................................................................................................................. 134

Trunk Encapsulation Methods ......................................................................................................... 135Configuring Trunk Ports ......................................................................................................................... 136Understanding and Configuring DTP ......................................................................................................137Verifying Port Configuration ................................................................................................................... 139

Verifying Access Ports .................................................................................................................... 139Verifying Trunk Ports ....................................................................................................................... 140

Understanding and Configuring VTP ..................................................................................................... 142VTP Domains .................................................................................................................................. 143VTP Version .................................................................................................................................... 144VTP Modes...................................................................................................................................... 145VTP Operation................................................................................................................................. 146VTP Pruning .................................................................................................................................... 148

Verifying VTP ......................................................................................................................................... 149Understanding InterVLAN Routing ........................................................................................................ 150

viii © 2012 Boson Software, LLC


Configuring InterVLAN Routing ..............................................................................................................151Troubleshooting VLANs and InterVLAN Routing ................................................................................... 153Review Question 1 ................................................................................................................................. 154Review Question 2 ................................................................................................................................. 156Review Question 3 ................................................................................................................................. 158Lab Exercises ........................................................................................................................................ 160

Module 7: Implementing STP .....................................................................................................161

Overview ................................................................................................................................................ 162Objectives .............................................................................................................................................. 162Understanding STP ................................................................................................................................ 163Root Switch Election ............................................................................................................................. 164Path Costs ............................................................................................................................................. 167Determining Port Roles .......................................................................................................................... 168

Root Port ......................................................................................................................................... 168Designated Port ............................................................................................................................... 168

STP Port States ..................................................................................................................................... 169STP Timers .............................................................................................................................................170Understanding RSTP ..............................................................................................................................171

Differences Between STP and RSTP ..............................................................................................172Understanding RSTP Port States .....................................................................................................173RSTP Alternate and Backup Port Roles ...........................................................................................174

Understanding Cisco Implementations of STP .......................................................................................175PVST+ ..............................................................................................................................................176PVRST+ ........................................................................................................................................... 177MSTP ................................................................................................................................................178

Cisco Enhancements to STP ..................................................................................................................179PortFast ........................................................................................................................................... 180BPDU Guard ....................................................................................................................................181Loop Guard...................................................................................................................................... 182Root Guard ...................................................................................................................................... 183

Review Question 1 ................................................................................................................................. 184Review Question 2 ................................................................................................................................. 186Lab Exercises ........................................................................................................................................ 188

Module 8: Implementing Switch Security .................................................................................189

Overview ................................................................................................................................................ 190Objectives .............................................................................................................................................. 190Establishing Written Security Policies ................................................................................................... 191Securing Access .................................................................................................................................... 192

Restricting Physical Access to the Switch ....................................................................................... 193Creating Secure Passwords for Console and Remote Access ....................................................... 194Creating a Secure Password for Privileged EXEC Mode Access ................................................... 195

ix© 2012 Boson Software, LLC


Encrypting Passwords on the Switch .............................................................................................. 196Securing, Disabling, or Replacing Vulnerable Services .................................................................. 197Configuring Warning Banners ......................................................................................................... 199

Securing Switch Ports............................................................................................................................ 200Disabling Unused Ports ................................................................................................................... 201Securing Trunk and Access Ports ................................................................................................... 202Restricting Ports by Client MAC Address ........................................................................................ 203Understanding 802.1X Port-based Authentication .......................................................................... 205How 802.1X Port-based Authentication Works .............................................................................. 206Configuring 802.1X Port-based Authentication ............................................................................... 207

Securing VLAN 1 ................................................................................................................................... 208Securing Spanning Tree Protocol .......................................................................................................... 209

Configuring Root Guard .................................................................................................................. 210Configuring BPDU Guard .................................................................................................................211Logging .............................................................................................................................................212Configuring Accurate Time ...............................................................................................................213Configuring Log Severity Levels .......................................................................................................214Configuring and Using a Logging Server .........................................................................................215

Review Question 1 ................................................................................................................................. 216Review Question 2 ..................................................................................................................................218Lab Exercises ........................................................................................................................................ 220

Module 9: Routing Fundamentals ..............................................................................................221

Overview ................................................................................................................................................ 222Objectives .............................................................................................................................................. 222Understanding Router Path Selection ................................................................................................... 223Understanding Static Routes ................................................................................................................. 224Understanding Dynamic Routes ............................................................................................................ 225Understanding AD.................................................................................................................................. 226Understanding Routing Metrics ............................................................................................................. 228Understanding Autonomous Systems.................................................................................................... 229Understanding Routing Protocols .......................................................................................................... 230Understanding the Types of IGPs .......................................................................................................... 231Understanding Distance-Vector Routing Protocols ............................................................................... 232

Learning Distance-Vector Routes ................................................................................................... 233Updating Distance-Vector Routes ................................................................................................... 234

Preventing Distance-Vector Problems ................................................................................................... 235Understanding the Counting to Infinity Problem .................................................................................... 236

Understanding Maximum Counts .................................................................................................... 238Understanding Routing Loops ............................................................................................................... 239

Preventing Routing Loops ............................................................................................................... 240Understanding Link-State Routing Protocols ..........................................................................................241

Learning Link-State Routes ............................................................................................................. 242

x © 2012 Boson Software, LLC


Review Question 1 ................................................................................................................................. 243Review Question 2 ................................................................................................................................. 245Lab Exercises ........................................................................................................................................ 247

Module 10 Implementing OSPF ..................................................................................................249

Overview ................................................................................................................................................ 250Objectives .............................................................................................................................................. 250Understanding OSPF ..............................................................................................................................251Understanding OSPF Areas .................................................................................................................. 252Understanding OSPF Router Roles ....................................................................................................... 253

Autonomous System Boundary Routers ......................................................................................... 253Area Border Routers ....................................................................................................................... 253Backbone and Nonbackbone Routers............................................................................................. 254

Configuring OSPF .................................................................................................................................. 255Verifying OSPF ...................................................................................................................................... 256Understanding OSPF Adjacencies ........................................................................................................ 258Verifying OSPF Adjacencies .................................................................................................................. 260Troubleshooting OSPF Adjacencies ...................................................................................................... 261Understanding DR and BDR Elections .................................................................................................. 262Using Cost to Load Balance OSPF........................................................................................................ 263Configuring OSPF Authentication .......................................................................................................... 264Review Question 1 ................................................................................................................................. 267Review Question 2 ................................................................................................................................. 269Review Question 3 ..................................................................................................................................271Lab Exercises ........................................................................................................................................ 273

Module 11: Implementing EIGRP ...............................................................................................275

Overview ................................................................................................................................................ 276Objectives .............................................................................................................................................. 276Understanding EIGRP ........................................................................................................................... 277

Choosing Between OSPF and EIGRP ............................................................................................ 278Understanding EIGRP Adjacencies ....................................................................................................... 279

Configuring Hello and Hold Timers ................................................................................................. 280Understanding EIGRP Path Selection ................................................................................................... 281

Understanding Advertised Distance and Feasible Distance ........................................................... 284Understanding EIGRP Tables ......................................................................................................... 286

Configuring EIGRP ................................................................................................................................ 288Verifying and Troubleshooting EIGRP ................................................................................................... 290Understanding EIGRP Load Balancing ................................................................................................. 292

Using Variance to Load Balance EIGRP ......................................................................................... 293Understanding EIGRP Route Summarization ........................................................................................ 295Understanding EIGRP Authentication ................................................................................................... 296Configuring EIGRP Authentication ........................................................................................................ 297

xi© 2012 Boson Software, LLC


Review Question 1 ................................................................................................................................. 299Review Question 2 ................................................................................................................................. 301Review Question 3 ................................................................................................................................. 303Review Question 4 ................................................................................................................................. 305Lab Exercises ........................................................................................................................................ 307

Module 12: Implementing PPP ...................................................................................................309

Overview .................................................................................................................................................310Objectives ...............................................................................................................................................310Implementing PPP ..................................................................................................................................311Establishing PPP Links ...........................................................................................................................312Configuring PPP on a Router Interface ..................................................................................................313Configuring PPP Authentication .............................................................................................................314

Configuring Router Host Names, User Names, and Passwords ......................................................315Configuring PAP Authentication .......................................................................................................316Configuring CHAP Authentication ....................................................................................................317Configuring PAP and CHAP on the Same Interface ........................................................................318

Review Question 1 ..................................................................................................................................319Review Question 2 ................................................................................................................................. 321Lab Exercises ........................................................................................................................................ 323

Module 13: Implementing Frame Relay .....................................................................................325

Overview ................................................................................................................................................ 326Objectives .............................................................................................................................................. 326Connecting to a Frame Relay Network .................................................................................................. 327Understanding Frame Relay Packets .................................................................................................... 328Understanding Virtual Circuits ............................................................................................................... 329Enabling Frame Relay ............................................................................................................................ 330Understanding Frame Relay Topologies ................................................................................................ 331

Full-Mesh Topology ......................................................................................................................... 331Partial-Mesh Topology .................................................................................................................... 332Hub-and-Spoke Topology ............................................................................................................... 333

Working Around Split Horizon ................................................................................................................ 334Configuring Subinterfaces ..................................................................................................................... 335

Configuring Point-to-Point Frame Relay .......................................................................................... 336Creating a Point-to-Point Subinterface ............................................................................................ 337Configuring Multipoint Frame Relay ................................................................................................ 338Creating a Multipoint Subinterface .................................................................................................. 339

Configuring Frame Relay Maps ............................................................................................................. 340Configuring Static Frame Relay Maps ............................................................................................. 341Automatic Frame Relay Map Configuration ..................................................................................... 342

Configuring LMI Signaling ...................................................................................................................... 343Configuring Inverse ARP ....................................................................................................................... 344

Configuring DLCIs .................................................................................................................................. 345Performing a Loopback Test .................................................................................................................. 346Review Question 1 ................................................................................................................................. 347Review Question 2 ................................................................................................................................. 349Lab Exercises ........................................................................................................................................ 351

Module 14: Implementing VPNs .................................................................................................353

Overview ................................................................................................................................................ 354Objectives .............................................................................................................................................. 354Understanding the Purpose of a VPN .................................................................................................... 355The Two Types of VPNs......................................................................................................................... 356

Understanding Site-to-Site VPNs .................................................................................................... 357Understanding Remote Access VPNs............................................................................................. 359

Understanding the IPSec Protocol ......................................................................................................... 361IPSec Encryption Methods .............................................................................................................. 362IPSec Data Integrity Methods ......................................................................................................... 363IPSec Authentication Methods ........................................................................................................ 364

Review Question 1 ................................................................................................................................. 365Review Question 2 ................................................................................................................................. 367

Index .............................................................................................................................................369

xii © 2012 Boson Software, LLC

1© 2012 Boson Software, LLC

Module 1Troubleshooting Networks

Module 1: Troubleshooting Networks

2 © 2012 Boson Software, LLC


Overview

No network is without issues, whether those issues are caused by a configuration error, an external attack, or even simple unexpected demands that do not fit the normal flow of traffic. Throughout this course, you will be provided with information about commands that can be helpful for troubleshooting IP addressing schemes, WAN networks, switches, routers, and the technologies that are implemented upon switches and routers. This module will introduce you to the usage of basic network troubleshooting techniques and commands that will help you understand how to apply the more specific commands that will be discussed later.

Objectives

After completing this module, you should have the basic knowledge required to complete all of the following tasks:

Implement a systematic network troubleshooting technique.Use show commands to monitor network operation.Use debug commands to monitor network traffic in real time.Use the ping command and the extended ping command.Use the traceroute command.

•••••



Understanding the Systematic Approach

There are several troubleshooting techniques you can use to isolate a problem. Whatever technique you use, you should implement the technique in a systematic, logical fashion. Unsystematic approaches to troubleshooting, such as making assumptions about the cause of a problem without gathering all the facts first, can lead to wasted time, can waste resources, and can make the problem worse.

When you are troubleshooting a problem on a network, Cisco recommends that you use the following systematic approach:

1. Define the problem: Because an end user cannot always reliably communicate the details of a technical problem, it is important to define the problem the user is experiencing in terms that are as technical as possible. Narrowing the technical definition of the problem can help you identify a starting point for your troubleshooting technique and immediately eliminate some possible causes of the problem. Ask the user a series of questions that are designed to narrow down the problem as much as possible.

2. Gather facts: After you have defined the problem, you should gather information about the problem by using troubleshooting tools, such as network sniffers, system logs, and output from show and debug commands. The information that is gathered from these tools can help pinpoint the location of a problem and narrow down the cause.

3. Consider the possibilities: Once you have gathered information about the problem, you should research the potential causes. Troubleshooting documentation, reference guides, and online user groups can all be sources of information about possible causes of a problem. After you consider the possibilities, you might discover that the original definition of the problem is not accurate. Therefore, you might need to return to the first step and define the problem again.



4. Create an action plan: After you define the problem and determine the cause, you should create a plan that details the steps you will take to solve the problem. In the plan, you should completely document the effects of any changes you intend to make to the configuration of the network or device. Stepping through the plan and knowing what you have and have not done will assist you in backing out any changes you make that negatively affect the network.

5. Implement an action plan: Once the creation of your action plan is complete, you should implement it in a step-by-step fashion. The first configuration changes you make while implementing your plan should be the changes that have only minimal effect on users, thus preventing unnecessary user downtime. You should also continue to document any changes you make and the effects of those changes on the network.

6. Observe results: After you make a change to the network, you should examine the results of that change before you make any other changes. If the change does not solve the original problem, could create other problems, or does not otherwise positively affect the network, you should back out the change and reconsider the possible causes of the original problem.

7. Document the solution: If you have solved the problem, you should document the solution step-by-step so that the solution is simple to implement or to back out when you next implement it. If you were not able to solve the problem, you should return to the second step in the process and begin gathering facts again.



Understanding Troubleshooting Techniques

Understanding the OSI Model

The Open Systems Interconnection (OSI) reference model is a conceptual representation of computer networking that is divided into the following seven layers:

Layer 7 – ApplicationLayer 6 – PresentationLayer 5 – SessionLayer 4 – TransportLayer 3 – NetworkLayer 2 – Data LinkLayer 1 – Physical

Individual layers of the OSI reference model can be referenced by name or by number. For example, the terms Data Link layer and Layer 2 are interchangeable when referring to the second layer of the OSI reference model. Technologies operating at each layer of the OSI model pass relevant information to technologies operating at adjacent layers. When information is passed down the OSI layers, each layer encapsulates the information with its own formatting and passes it to the next-lower layer; eventually, the information is transmitted as bits at the Physical layer. When information is passed up the OSI layers, each layer removes its formatting and organizes the information so that it can be interpreted by the next-higher layer.

•••••••



Implementing the OSI Techniques

Understanding the Bottom Up Troubleshooting Technique

The bottom up method of network troubleshooting begins at the Physical layer of the OSI reference model and works through the other layers, one-by-one, toward the Application layer until the problem is isolated. For example, an administrator who is troubleshooting a workstation that can no longer connect to the network might choose to first check the workstation’s physical connection to the network, such as checking for a loose cable. If the cable is not loose, the administrator might decide to proceed to the Data Link layer of the OSI reference model, then to the Network Layer, and so on.

Understanding the Top Down Troubleshooting Technique

The top down troubleshooting technique starts at the Application layer and works toward the Physical layer of the OSI reference model. An administrator using the top down method of network troubleshooting might begin the process by examining or restarting the network applications on a workstation that has lost connectivity to the network.



Understanding the Divide and Conquer Troubleshooting Technique

The divide and conquer troubleshooting technique starts at the Network layer and works either up or down the OSI model depending on the outcome of network tests, such as the ping command. For example, an administrator who is using the divide and conquer method to troubleshoot a workstation that has lost connectivity to the network might receive a successful reply to a ping command from that workstation and, based on that result, might decide to move on to the Transport layer of the OSI model. However, an administrator who does not receive a successful reply to the ping command from the workstation might choose to check for a valid IP address at the Network layer, then for a port-security or Spanning Tree Protocol (STP) problem at the Data Link layer, and then for a cable-connection problem at the Physical layer.



Implementing the Non-OSI Techniques

Understanding the Follow the Path Troubleshooting Technique

The follow the path troubleshooting technique is a packet-examination method of network troubleshooting. An administrator who chooses to use the follow the path method might issue a traceroute command to determine the location of a broken hop in a route. For example, if a traceroute command that is issued from a workstation that has lost connectivity to the network ends at a device that is two hops away from the workstation, the problem is most likely located on or beyond the device two hops away, not on the workstation.

Understanding the Move the Problem Troubleshooting Technique

The move the problem troubleshooting technique is the process of replacing components to determine whether the problem remains on the original device or moves with the suspect component. For example, an administrator who suspects that a bad Ethernet cable is the cause of a loss of network connectivity might choose to replace the cable with a known good one. If the known good cable restores network connectivity on the affected device, the original cable is most likely bad and should be permanently replaced with a known good cable.



Understanding the Spot the Difference Troubleshooting Technique

The spot the difference troubleshooting technique is the process of comparing a faulty configuration with a known good configuration. An administrator who uses the spot the difference method might look for differences in the two configurations that could cause or contribute to the loss of network connectivity. For example, an administrator who is troubleshooting a workstation that cannot connect to the network might choose to compare the IP address configuration of a computer that can connect to the network with the IP address configuration of the affected workstation.



Understanding show Commands

IOS show commands provide information about a device or network activity that is static or collected over a period of time. The commands can be helpful in isolating configuration problems, detecting network congestion, or displaying the current status of a device or its components. You should typically issue show commands in privileged EXEC mode.

Commands such as show ip route and show spanning-tree display information related to the normal network operation of a Cisco device. The show ip route command displays a router’s routing table. The show spanning-tree command displays STP information on a switch.

Commands such as show cdp neighbors provide status information. The show cdp neighbors command provides information based on data gathered by Cisco Discovery Protocol (CDP) about devices that are connected to the device on which you issue the command. You can use show cdp neighbors to help troubleshoot Layer 1 and Layer 2 problems on a device.

Commands such as show interfaces and show controllers provide statistics about a device. The show interfaces command displays statistics about a single interface or all the interfaces on a device, depending on how the command is issued. The show controllers command displays statistics about interface card controllers. For example, you can use show controllers to determine which side of a serial connection is the data terminal equipment (DTE) side and which is the data communications equipment (DCE) side.

Some show commands provide more static information about a device. For example, the show version command provides information about the version of IOS that is running on a Cisco device. You can also use show version to determine whether enough RAM exists on the device to support an IOS upgrade and to view



the configuration register, which determines the order of the device boot process. Similarly, the show flash command provides memory usage information and displays the contents of Flash memory.

Other show commands that provide static information are show running-config, which displays the device configuration that is currently loaded in memory, and show startup-config, which displays the device configuration that will be loaded the next time the device is restarted or the configuration is reloaded.



Understanding debug Commands

IOS debug commands enable an administrator to view traffic and information in real time, as it happens on the device. However, debug commands can significantly increase the use of device resources and can degrade performance. Therefore, you should use debug commands only to troubleshoot a problem, not to monitor normal network traffic.

You should typically issue debug commands from privileged EXEC mode. After you have gathered all the information you need from the output of a debug command, you can disable debugging by issuing the no form of the specific debug command, or by issuing the no debug all command in privileged EXEC mode.

You can take steps to minimize the effects of debug commands on device performance. For example, you can issue the no logging console command to disable the echoing of debugging output to the console. Logging debugging output to the console increases the CPU load on the device. After you disable logging to the console, you can issue the terminal monitor command to display debugging output to the Telnet or Secure Shell (SSH) session you use to connect to the device.



Understanding the ping Command

The ping command is one of the most common network troubleshooting tools. A version of the ping command exists on Microsoft Windows, on Mac OS X, and on typical Linux distributions. The ping command can be used to test a host’s connection to the network by sending Internet Control Message Protocol (ICMP) Echo messages to another host’s IP address. If the source host receives an ICMP Echo Reply message from the remote host, the ping command has verified two things: that the source host is connected to the network and that the remote host is reachable on the network.

The ping command is typically issued with a single parameter, which is the IP address or Domain Name System (DNS) host name of the remote host that you want to ping. On workstation operating systems such as Microsoft Windows, you can also issue the ping 127.0.0.1 or ping localhost command to determine whether the Transmission Control Protocol (TCP)/IP stack has been successfully installed on the workstation.

The IOS version of ping works similarly to the versions that exist on other operating systems. However, if you issue the ping command from the Cisco IOS without parameters, IOS enters extended ping mode. Extended ping mode provides a series of prompts for information about how you want to issue the ping command. For example, you can choose to use a protocol other than IP, choose a different timeout value other than the 2-second default, and you can enter the number of times the command should repeat its attempt to communicate with the remote host. If you issue the ping command in normal mode, IOS will ping the remote device five times. You should issue the ping command from privileged EXEC mode.



Understanding the traceroute Command

Similar to the ping command, the traceroute command is another troubleshooting tool that is common across platforms. The traceroute command is designed to trace the route of a packet from a source to a destination. The information that is provided by the traceroute command is useful in helping to determine where problems exist along a path to a destination. The syntax of the traceroute command is traceroute host, where host is the IP address or DNS host name of a remote device. For example, if you wanted to trace a packet from a source host to boson.com, you would issue the traceroute boson.com command in privileged EXEC mode.

The traceroute command works by sending User Datagram Protocol (UDP) traffic with a time to live (TTL) value of 1 to an invalid port number at a remote host. The low TTL causes the device at each hop, or router, along the path to the destination to reply to the UDP traffic with an ICMP Time Exceeded Message (TEM), which means that the device at the hop received and discarded the UDP traffic. The source host then sends additional probes to the device at the hop. The TTL is increased by 1 after every third probe. The IP address of the device at the hop is used by the source host to build a list of hops until the UDP traffic finally reaches its destination, at which point the destination host will send a Destination Unreachable message. The Destination Unreachable message means that the destination received the traffic but was unable to direct it to a valid UDP port. The traceroute command will display the * symbol if the timer expires before it receives either a TEM or a Destination Unreachable message from a device at a hop or from the destination device.

Similar to the extended ping command, there is an extended form of the traceroute command that enables you to specify a protocol other than IP, change the default timeout, change the probe count, and change the maximum TTL. It is important to note that setting a maximum TTL that is too low can cause the traceroute command to time out before the UDP traffic reaches its destination.



Review Question 1



There are several troubleshooting techniques you can use to isolate a problem. Whatever technique you use, you should implement the technique in a systematic, logical fashion. Unsystematic approaches to troubleshooting, such as making assumptions about the cause of a problem without gathering all the facts first, can lead to wasted time, wasted resources, and a worse problem. When you are troubleshooting a problem on a network, Cisco recommends that you begin by defining the problem.

Because an end user cannot always reliably communicate the details of a technical problem, it is important to define the problem the user is experiencing in terms that are as technical as possible. Narrowing the technical definition of the problem can help you identify a starting point for your troubleshooting technique and immediately eliminate some possible causes of the problem. Ask the user a series of questions that are designed to narrow down the problem as much as possible.



Review Question 2



The ping command is one of the most common network troubleshooting tools. The ping command can be used to test a host’s connection to the network by sending Internet Control Message Protocol (ICMP) Echo messages to another host’s IP address. If the source host receives an ICMP Echo Reply message from the remote host, the ping command has verified two things: that the source host is connected to the network and that the remote host is reachable on the network.

The traceroute command works by sending User Datagram Protocol (UDP) traffic with a time to live (TTL) value of 1 to a remote host. The low TTL causes the device at each hop, or router, along the path to the destination to reply to the UDP traffic with an ICMP Time Exceeded Message (TEM), which means that the device at the hop received and discarded the UDP traffic. The source host then sends additional probes to the device at the hop. The TTL is increased by 1 after every third probe. The IP address of the device at the hop is used by the source host to build a list of hops until the UDP traffic finally reaches its destination, at which point the destination host will send a Destination Unreachable message. The Destination Unreachable message means that the destination received the traffic but was unable to direct it to a valid UDP port. The traceroute command will display the * symbol if the timer expires before it receives either a TEM or a Destination Unreachable message from a device at a hop or from the destination device.



Review Question 3



The top down troubleshooting technique starts at the Application layer and works toward the Physical layer of the Open Systems Interconnection (OSI) reference model. An administrator using the top down method of network troubleshooting might begin the process by examining or restarting the network applications on a workstation that has lost connectivity to the network.

The bottom up method of network troubleshooting begins at the Physical layer of the OSI reference model and then works through the other layers, one-by-one, toward the Application layer until the problem is isolated. For example, an administrator who is troubleshooting a workstation that can no longer connect to the network might choose to first check the workstation’s physical connection to the network, such as checking for a loose cable. If the cable is not loose, the administrator might decide to proceed to the Data Link layer of the OSI reference model, then to the Network Layer, and so on.

The divide and conquer troubleshooting technique starts at the Network layer and works either up or down the OSI model depending on the outcome of network tests, such as the ping command. For example, an administrator who is using the divide and conquer method to troubleshoot a workstation that has lost connectivity to the network might receive a successful reply to a ping command from that workstation and, based on that result, might decide to move on to the Transport layer of the OSI model. However, an administrator who does not receive a successful reply to the ping command from the workstation might choose to check for a valid IP address at the Network layer, then for a port-security or Spanning Tree Protocol (STP) problem at the Data Link layer, and then for a cable-connection problem at the Physical layer.



Lab Exercises

Organizational and Volume Customers

Boson Software’s outstanding IT training tools serve the skill development needs of organizations such as colleges, technical training educators, corporations, and governmental agencies. If your organization would like to inquire about volume opportunities and discounts, please contact Boson Software at [email protected].

Contact Information

E-Mail: [email protected]: 877-333-EXAM (3926) 615-889-0121Fax: 615-889-0122Address: 25 Century Blvd. Ste. 500 Nashville, TN 37214

© C o py r ig h t 2012 Bo s o n Sof t wa r e , LL C. A l l r ig h t s r e s e r ve d . 3 -15 -12

b o s o n . c o m8 7 7 . 3 3 3 . 3 9 2 6 s u p p o r t @ b o s o n . c o m

ICND 2 Promo - Boson Frame Relay.....330 Understanding Frame Relay Topologies..... 331 Full-Mesh...

Documents

Transcript of ICND 2 Promo - Boson Frame Relay.....330 Understanding Frame Relay Topologies..... 331 Full-Mesh...