Troubleshooting an Enterprise Network

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.