1. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE I Chapter 6 1 Troubleshooting an Enterprise Network Introducing Routing and Switching in the Enterprise – Chapter 9

2. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 2 Objectives  Explain the importance of uptime and the types of issues that cause failure.  Isolate and correct switching problems.  Isolate and correct routing issues.  Isolate and correct WAN configurations.  Isolate and correct ACL issues.

3. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 3 Explain the Importance of Uptime and the Types of Issues that Cause Failure  Reduction in uptime can have a negative impact on a business  Downtime results in lost productivity and customer frustration

4. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 4 Explain the Importance of Uptime and the Types of Issues that Cause Failure Ways to ensure uptime:  Proactive maintenance  Network monitoring

5. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 5 Explain the Importance of Uptime and the Types of Issues that Cause Failure  Failure domain: area of the network affected by the failure or misconfiguration of a network device  Troubleshoot resources with a larger failure domain first, unless another problem is business critical

6. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 6 Explain the Importance of Uptime and the Types of Issues that Cause Failure Troubleshooting approaches:  Top-down  Bottom-up  Divide and conquer  Trial and error  Substitution

7. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 7 Isolate and Correct Switching Problems  The most common problems with switches occur at the Physical Layer

8. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 8 Isolate and Correct Switching Problems  Suboptimal switching can be traced to STP problems  Determine the VLAN assignment of non-functioning ports  Verify the trunking protocol if inter-VLAN routing is required

9. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 9 Isolate and Correct Switching Problems  Verify VTP domain name  Verify identical revision numbers on all devices  Verify identical VTP versions on all devices

10. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 10 Isolate and Correct Routing Issues Determining and correcting RIP issues:  Compatibility between RIPv1 and RIPv2  Missing or incorrect network statements  Errors in interface configurations

11. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 11 Isolate and Correct Routing Issues Determine and correct EIGRP issues:  Mismatched AS numbers  Errors in network statements  Errors in interface addressing  Auto-summarization used with discontiguous subnets

12. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 12 Isolate and Correct Routing Issues Determine and correct OSPF issues:  Mismatched authentication or timer intervals  Errors in wildcard masks or network statements  Errors in interface configurations

13. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 13 Isolate and Correct Routing Issues  Determine and correct route redistribution  Verify that users on internal routers can access external networks

14. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 14 Isolate and Correct WAN Configurations  Clocking  Cable types  Loose or faulty connectors Determine and correct WAN Physical Layer connection issues:

15. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 15 Isolate and Correct WAN Configurations Determine and correct WAN Data Link Layer and Network Layer connection issues:  Encapsulation mismatches  Incompatible formats  IP addressing errors

16. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 16 Isolate and Correct WAN Configurations  Determine and correct authentication issues

17. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 17 Isolate and Correct ACL Issues  Verify network connectivity before an ACL is applied  Enable logging

18. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 18 Isolate and Correct ACL Issues Determine and correct ACL configuration and placement issues:  ACL statements should permit highest volume traffic early in the ACL  Implicit deny may have unintended consequences  Improper ACL placement may waste bandwidth

19. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 19 Summary  Adherence to the three-layer hierarchical network design model assists in troubleshooting  When troubleshooting a network, determine the scope of the problem and isolate the issue to a specific failure domain.  The most common problems with switches occur at the Physical Layer.  Use debug commands to isolate problems, not to monitor normal network operation.  When troubleshooting PPP, verify that the LCP has been opened, authentication and NCP completed.  ACLs can create complications in network operations.

20. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 20