Troubleshooting

1. Troubleshooting Working at a Small-to-Medium Business or ISP � Chapter 9

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.

3. Troubleshooting Methodologies and Tools Knowledge of the features, functions and devices of each OSI or TCP/IP layer supports efficient troubleshooting

4. Three troubleshooting approaches: Top-down Bottom-up Divide-and-conquer Troubleshooting Methodologies and Tools

5. Helpful network diagrams: Physical network topology Logical network topology Troubleshooting Methodologies and Tools

6. Additional troubleshooting tools: Documentation and baseline tools Management system tools Knowledge bases Protocol analyzers Troubleshooting Methodologies and Tools

7. Hardware troubleshooting tools: Cable testers Digital multimeters Portable network analyzers Troubleshooting Methodologies and Tools

8. Layer 1 problems are related to the type of technology used Layer 1 problems can result in loss of connectivity or degraded network performance Troubleshooting Layer 1 and Layer 2 Issues

9. Troubleshooting Layer 1 and Layer 2 Issues Layer 2 specifies data format and network access Network analyzers can diagnose Layer 2 issues

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

11. Five common bootup errors: POST failure Corrupt flash image Corrupt or missing configuration file Memory error Module error Troubleshooting Layer 1 and Layer 2 Issues

12. Troubleshooting Layer 1 and Layer 2 Issues Common issues causing up/down or down/down outputs: Loose or incorrectly terminated cables Damaged interface or cable Improper encapsulation configuration

13. Use output from the show interfaces command to help identify media errors: Excessive noise Excessive collisions Excessive runts Late collisions Troubleshooting Layer 1 and Layer 2 Issues

14. Troubleshooting LAN connectivity on switches: Observe port LEDs Verify cables Verify configuration Verify duplex settings Troubleshooting Layer 1 and Layer 2 Issues

15. Troubleshooting WAN connectivity issues: Use show interfaces serial output Know the type of modem or CSU/DSU being used Troubleshooting Layer 1 and Layer 2 Issues

16. Many Layer 3 problems are due to poorly designed and configured IP addressing schemes Determine the host range in order to troubleshoot Troubleshooting Layer 3 IP Addressing Issues

17. Problems resulting from poor Layer 3 planning: Overlapping subnets Misconfigured subnet masks Insufficient addresses available through DHCP Troubleshooting Layer 3 IP Addressing Issues

18. DHCP issues: Physical connectivity Server misconfiguration Address conflicts Troubleshooting Layer 3 IP Addressing Issues

19. NAT issues: Incorrect designation of inside and outside interfaces Pool misconfiguration No route to the Internet for translated addresses Troubleshooting Layer 3 IP Addressing Issues

20. Common routing issues: Manual route entry errors Routing protocol configuration errors Failures at lower OSI layers Troubleshooting Layer 3 Routing Issues

21. The routing table indicates connected, dynamic, static and default routes Troubleshooting Layer 3 Routing Issues

22. Issues related to RIP: Version mismatch Incorrect or missing network statements Troubleshooting Layer 3 Routing Issues

23. Tools for troubleshooting dynamic routing issues: TCP/IP utilities Debug commands Troubleshooting Layer 3 IP Addressing Issues

24. Traffic filtering issues: Firewall misconfiguration Incorrect port assignment Troubleshooting Layer 4 and Upper Layer Issues

25. 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 Troubleshooting Layer 4 and Upper Layer Issues

26. 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 Troubleshooting Layer 4 and Upper Layer Issues

27. Telnet provides troubleshooting access, but is an insecure protocol SSH is a more secure method for remote device access Troubleshooting Layer 4 and Upper Layer Issues

28. ICND1 exam (640-822) includes topics on networking fundamentals Pass ICND1 to achieve CCENT certification Preparing for Cisco Certification

29. What certification exams measure: Knowledge: facts recalled from memory Skills: interacting with Cisco networking devices Abilities: scenario-based or simulation tasks Preparing for Cisco Certification

30. Make the commitment Create a study plan Practice test taking Preparing for Cisco Certification

31. Visit the testing center Become familiar with the test format Use exam tutorials and practice tests Practice Packet Tracers and labs Preparing for Cisco Certification

32. 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. Summary