CCNA Discovery 2 - Chapter 9

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CCNA Discovery 2 - Chapter 9

  1. 1. Troubleshooting Working at a Small-to-Medium Business or ISP – Chapter 9Version 4.1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1
  2. 2. Objectives Use the OSI model as a framework for troubleshooting network problems. Identify and correct problems with hardware and operation at Layer 1 and Layer 2. Troubleshoot IP addressing problems, including subnet mask, host range errors, DHCP and NAT issues. Identify and correct problems with RIPv2 configuration and implementation. Explain possible causes of problems occurring with user applications and how to recognize symptoms of DNS failures. Create a plan to prepare to take the ICND1 examination in order to obtain a CCENT certification. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 2
  3. 3. Troubleshooting Methodologies and Tools Knowledge of the features, functions and devices of each OSI or TCP/IP layer supports efficient troubleshooting © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 3
  4. 4. Troubleshooting Methodologies and ToolsThree troubleshooting approaches: Top-down Bottom-up Divide-and-conquer © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 4
  5. 5. Troubleshooting Methodologies and ToolsHelpful network diagrams: Physical network topology Logical network topology © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 5
  6. 6. Troubleshooting Methodologies and ToolsAdditional troubleshooting tools: Documentation and baseline tools Management system tools Knowledge bases Protocol analyzers © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 6
  7. 7. Troubleshooting Methodologies and ToolsHardware troubleshooting tools: Cable testers Digital multimeters Portable network analyzers © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 7
  8. 8. Troubleshooting Layer 1 and Layer 2 Issues Layer 1 problems are related to the type of technology used Layer 1 problems can result in loss of connectivity or degraded network performance © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 8
  9. 9. Troubleshooting Layer 1 and Layer 2 Issues Layer 2 specifies data format and network access Network analyzers can diagnose Layer 2 issues © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 9
  10. 10. Troubleshooting Layer 1 and Layer 2 Issues Observe console messages during the boot sequence Use Cisco IOS CLI show commands to verify operational status When boot problems cause a network outage, use substitution to restore service © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 10
  11. 11. Troubleshooting Layer 1 and Layer 2 IssuesFive common bootup errors: POST failure Corrupt flash image Corrupt or missing configuration file Memory error Module error © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 11
  12. 12. Troubleshooting Layer 1 and Layer 2 IssuesCommon issues causing up/down or down/down outputs: Loose or incorrectly terminated cables Damaged interface or cable Improper encapsulation configuration © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 12
  13. 13. Troubleshooting Layer 1 and Layer 2 IssuesUse output from the show interfaces command to help identify media errors: Excessive noise Excessive collisions Excessive runts Late collisions © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 13
  14. 14. Troubleshooting Layer 1 and Layer 2 IssuesTroubleshooting LAN connectivity on switches: Observe port LEDs Verify cables Verify configuration Verify duplex settings © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 14
  15. 15. Troubleshooting Layer 1 and Layer 2 IssuesTroubleshooting WAN connectivity issues: Use show interfaces serial output Know the type of modem or CSU/DSU being used © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 15
  16. 16. Troubleshooting Layer 3 IP Addressing Issues Many Layer 3 problems are due to poorly designed and configured IP addressing schemes Determine the host range in order to troubleshoot © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 16
  17. 17. Troubleshooting Layer 3 IP Addressing IssuesProblems resulting from poor Layer 3 planning: Overlapping subnets Misconfigured subnet masks Insufficient addresses available through DHCP © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 17
  18. 18. Troubleshooting Layer 3 IP Addressing IssuesDHCP issues: Physical connectivity Server misconfiguration Address conflicts © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 18
  19. 19. Troubleshooting Layer 3 IP Addressing IssuesNAT issues: Incorrect designation of inside and outside interfaces Pool misconfiguration No route to the Internet for translated addresses © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 19
  20. 20. Troubleshooting Layer 3 Routing IssuesCommon routing issues: Manual route entry errors Routing protocol configuration errors Failures at lower OSI layers © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 20
  21. 21. Troubleshooting Layer 3 Routing Issues The routing table indicates connected, dynamic, static and default routes © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 21
  22. 22. Troubleshooting Layer 3 Routing IssuesIssues related to RIP: Version mismatch Incorrect or missing network statements © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 22
  23. 23. Troubleshooting Layer 3 IP Addressing IssuesTools for troubleshooting dynamic routing issues: TCP/IP utilities Debug commands © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 23
  24. 24. Troubleshooting Layer 4 and Upper Layer IssuesTraffic filtering issues: Firewall misconfiguration Incorrect port assignment © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 24
  25. 25. Troubleshooting Layer 4 and Upper Layer Issues Basic connectivity must be eliminated as the source of the problem Check with the ISP to ensure that the problem does not lie with the remote network © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 25
  26. 26. Troubleshooting Layer 4 and Upper Layer Issues Upper layer issues can exist even with full network connectivity Check application configuration with specific problems Encryption or compression mismatch may be an issue Make sure browser plug-ins have been updated If more than one application is affected, a DNS server issue may be the problem © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 26
  27. 27. Troubleshooting Layer 4 and Upper Layer Issues Telnet provides troubleshooting access, but is an insecure protocol SSH is a more secure method for remote device access © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 27
  28. 28. Preparing for Cisco Certification ICND1 exam (640-822) includes topics on networking fundamentals Pass ICND1 to achieve CCENT certification © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 28
  29. 29. Preparing for Cisco CertificationWhat certification exams measure: Knowledge: facts recalled from memory Skills: interacting with Cisco networking devices Abilities: scenario-based or simulation tasks © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 29
  30. 30. Preparing for Cisco Certification Make the commitment Create a study plan Practice test taking © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 30
  31. 31. Preparing for Cisco Certification Visit the testing center Become familiar with the test format Use exam tutorials and practice tests Practice Packet Tracers and labs © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 31
  32. 32. Summary Networking models provide a framework for efficient troubleshooting. Good troubleshooting involves using a methodology, such as top-down, bottom-up, or divide-and-conquer. The majority of Layer 3 problems result from poor or incorrect addressing schemes. Firewall misconfiguration can result in problems with upper layer protocols. Success on certification tests depends on building knowledge, skills, and abilities. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 32
  33. 33. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 33

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