cn instructorppt chapter9 final
TRANSCRIPT
© 2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 1
Chapter 9: Troubleshooting the Network
Connecting Networks
Presentation_ID 2© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 99.0 Introduction
9.1 Troubleshooting with a Systematic Approach
9.2 Network Troubleshooting
9.3 Summary
© 2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 3
9.1 Troubleshooting with a Systematic Approach
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Chapter 9: Objectives Explain how network documentation is developed and used to
troubleshoot network issues. Describe the general troubleshooting process. Compare troubleshooting methods that use a systematic, layered
approach. Describe troubleshooting tools used to gather and analyze
symptoms of network problems. Determine the symptoms and causes of network problems using a
layered model. Troubleshoot a network using the layered model.
Presentation_ID 5© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Network DocumentationDocumenting the NetworkNetwork documentation is a complete set of accurate and current network documentation. This documentation includes: Configuration files, including network configuration files and end-
system configuration files Physical and logical topology diagrams A baseline performance level
Presentation_ID 6© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Network DocumentationNetwork Topology Diagrams
Physical TopologyDevice type
Model and manufacturer
Operating system versionCable type and
identifierCable specification
Connector typeCabling endpoints
Logical TopologyDevice identifiers
IP address and prefix lengths
Interface identifiersConnection type
DLCI for virtual circuitsSite-to-site VPNs
Routing protocolsStatic routes
Data-link protocolsWAN technologies
used
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Network DocumentationEstablishing a Network Baseline
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Network DocumentationEstablishing a Network Baseline (cont.)
Step 1. Determine what types of data to collect.
Step 2. Identify devices and ports of interest.
Step 3. Determine the baseline duration.
Presentation_ID 9© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Network DocumentationMeasuring Data
Commands that are useful to the network documentation process include: ping telnet show ip interface brief show ipv6 interface brief show ip route show ipv6 route show cdp neighbor detail
Presentation_ID 10© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting ProcessGeneral Troubleshooting Procedures
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Troubleshooting ProcessGathering Symptoms
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Troubleshooting ProcessQuestioning End Users
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Isolating the Issue Using Layered ModelsUsing Layered Models for Troubleshooting
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Isolating the Issue Using Layered ModelsTroubleshooting MethodsUsing the layered models, there are three primary methods for troubleshooting networks: Bottom-up Top-down Divide-and-conquer
Presentation_ID 15© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Isolating the Issue Using Layered ModelsTroubleshooting Methods (cont.)In addition to the systematic, layered approach to troubleshooting, there are also, less-structured troubleshooting approaches: One troubleshooting approach is based on an educated guess by
the network administrator, based on the symptoms of the problem. Another approach involves comparing a working and nonworking
situation, and spotting significant differences. Swapping the problematic device with a known, working one is a
quick way to troubleshoot.
Presentation_ID 16© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Isolating the Issue Using Layered ModelsGuidelines for Selecting a Troubleshooting Method
© 2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 17
9.2 Network Troubleshooting
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Troubleshooting ToolsSoftware Troubleshooting ToolsCommon software troubleshooting tools include: NMS tools Knowledge bases Baselining tools Host-based protocol analyzers Cisco IOS EPC
Presentation_ID 19© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting ToolsHardware Troubleshooting ToolsCommon hardware troubleshooting tools include: Network analysis module Digital multimeters Cable testers Cable analyzers Portable network analyzers
Presentation_ID 20© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting ToolsUsing a Syslog Server for Troubleshooting
Severity Level
Presentation_ID 21© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Symptoms and Causes of Network TroubleshootingPhysical Layer Troubleshooting
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Symptoms and Causes of Network TroubleshootingData Link Layer Troubleshooting
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Symptoms and Causes of Network TroubleshootingNetwork Layer Troubleshooting
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Symptoms and Causes of Network TroubleshootingTransport Layer Troubleshooting – ACLs
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Symptoms and Causes of Network TroubleshootingTransport Layer Troubleshooting – NAT for IPv4
Presentation_ID 26© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Symptoms and Causes of Network TroubleshootingApplication Layer Troubleshooting
Presentation_ID 27© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityComponents of Troubleshooting End-to-End ConnectivityWhen there is no end-to-end connectivity, and the administrator chooses to troubleshoot with a bottom-up approach, these are common steps the administrator can take:
Step 1. Check physical connectivity at the point where network communication stops, including cables and hardware. The problem might be with a faulty cable or interface, or involve misconfigured or faulty hardware.
Step 2. Check for duplex mismatches.
Step 3. Check data link and network layer addressing on the local network. This includes IPv4 ARP tables, IPv6 neighbor tables, MAC address tables, and VLAN assignments.
Presentation_ID 28© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityComponents of Troubleshooting End-to-End Connectivity (cont.)
Step 4. Verify that the default gateway is correct.
Step 5. Ensure that devices are determining the correct path from the source to the destination. Manipulate the routing information if necessary.
Step 6. Verify that the transport layer is functioning properly. Telnet can also be used to test transport layer connections from the command line.
Step 7. Verify that there are no ACLs blocking traffic.
Step 8. Ensure that DNS settings are correct. There should be an accessible DNS server.
Presentation_ID 29© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityEnd-to-End Connectivity Problem Initiates Troubleshooting
Presentation_ID 30© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 1. Verify the Physical Layer
Presentation_ID 31© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 2. Check for Duplex Mismatches
Presentation_ID 32© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 3. Verify Layer 2 and Layer 3 Addressing on the Local Network
IPv4: arp command (PC) show mac address-table command (router)
IPv6: netsh interface ipv6 show neighbor command (PC)
show ipv6 neighbors (router)
Presentation_ID 33© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 4. Verify Default Gateway
Presentation_ID 34© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 5. Verify Correct Path
Presentation_ID 35© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 6. Verify the Transport Layer
Presentation_ID 36© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 7. Verify ACLs
Presentation_ID 37© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Troubleshooting IP ConnectivityStep 8. Verify DNS
Presentation_ID 38© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 9: Summary
Presentation_ID 39© 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential