1. Troubleshooting an Enterprise Network
Introducing Routing and Switching in the Enterprise – Chapter 9

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. 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. Explain the Importance of Uptime and the Types of Issues that Cause Failure
Ways to ensure uptime:
Proactive maintenance
Network monitoring

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. 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. Isolate and Correct Switching Problems
The most common problems with switches occur at the Physical Layer

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. Isolate and Correct Switching Problems
Verify VTP domain name
Verify identical revision numbers on all devices
Verify identical VTP versions on all devices

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. 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. 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. Isolate and Correct Routing Issues
Determine and correct route redistribution
Verify that users on internal routers can access external networks

14. Isolate and Correct WAN Configurations
Determine and correct WAN Physical Layer connection issues:
Clocking
Cable types
Loose or faulty connectors

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. Isolate and Correct WAN Configurations
Determine and correct authentication issues

17. Isolate and Correct ACL Issues
Verify network connectivity before an ACL is applied
Enable logging

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. 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.