Some possible reasons why EIGRP may not be working correctly are:

• Layer 1 or Layer 2 connectivity issues exist.
• Autonomous system numbers on EIGRP routers are mismatched.
• The link may be congested or down.
• The outgoing interface is down.
• The advertised network interface is down.
• Auto-summarization is enabled on routers with discontiguous subnets.
• Use no auto-summary to disable automatic network summarization.

One of the most common reasons for a missing neighbor is a failure on the actual link. Another possible cause of missing neighbors is an expired holddown timer. Since hellos are sent every 5 seconds on most networks, the hold-time value in a show ip eigrp neighbors command output should normally be a value between 10 and 15. To effectively monitor and troubleshoot an EIGRP network, use the commands described in Figures - . Web Links Troubleshooting EIGRP http://www.cisco.com/en/US/tech/
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Content 3.3 Troubleshooting Routing Protocols 3.3.5 Troubleshooting OSPF configuration Open Shortest Path First (OSPF) is a link-state protocol. A link is an interface on a router. The state of the link is a description of that interface and of its relationship to its neighboring routers. For example, a description of the interface would include the IP address, the mask, the type of network to which it is connected, the routers connected to that network, and so on. This information forms a link-state database.The majority of problems encountered with OSPF relate to the formation of adjacencies and the synchronization of the link-state databases. The show ip ospf neighbor command is useful for troubleshooting adjacency formation. OSPF configuration commands are shown in Figure . Use the debug ip ospf events privileged EXEC command to display the following information about OSPF-related events:

• Adjacencies
• Flooding information
• Designated router selection
• Shortest path first (SPF) calculation

If a router configured for OSPF routing is not seeing an OSPF neighbor on an attached network, perform the following tasks:

• Verify that both routers have been configured with the same IP mask, OSPF hello interval, and OSPF dead interval.
• Verify that both neighbors are part of the same area.

To display information about each Open Shortest Path First (OSPF) packet received, use the debug ip ospf packet privileged EXEC command. The no form of this command disables debugging output. The debug ip ospf packet command produces one set of information for each packet received. The output varies slightly, depending on which authentication is used. Web Links Troubleshooting OSPF http://www.cisco.com/en/US/tech/
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Content Summary An understanding of the following key points should have been achieved:

• Differences between EIGRP and IGRP
• Key concepts, technologies, and data structures of EIGRP
• EIGRP convergence and the basic operation of the Diffusing Update Algorithm, or DUAL
• Basic EIGRP configuration
• Configuring EIGRP route summarization
• The processes used by EIGRP to build and maintain routing tables
• Verifying EIGRP operations
• The eight-step process for general troubleshooting
• Applying a logical process to routing troubleshooting
• Troubleshooting a RIP routing process using show and debug commands
• Troubleshooting an IGRP routing process using show and debug commands
• Troubleshooting an EIGRP routing process using show and debug commands
• Troubleshooting an OSPF routing process using show and debug commands