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

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.

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

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

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

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

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

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

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

Isolate and Correct Routing Issues Determining and correcting RIP issues: Compatibility between RIPv1 and RIPv2 Missing or incorrect network statements Errors in interface configurations

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

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

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

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

Isolate and Correct WAN Configurations Determine and correct WAN Data Link Layer and Network Layer connection issues: Encapsulation mismatches Incompatible formats IP addressing errors

Isolate and Correct WAN Configurations Determine and correct authentication issues

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

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

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.