EIGRP Interview - This was asked in Fivesky interview

The network uses EIGRP as its routing protocol. The network administrator is experiencing intermittent connectivity issues between certain sites. The network topology includes multiple distribution and core switches, and there are several potential points of failure, including redundant links and alternate paths. Explain in detail how you would diagnose and troubleshoot these connectivity issues, considering EIGRP’s features, such as split-horizon, feasible successor routes, EIGRP metrics, route summarization, and authentication. Provide step-by-step guidance on analyzing EIGRP’s topology table, routing table, and neighbor relationships to identify the root cause of the problem. Additionally, discuss how you would use debugging tools, such as EIGRP packet captures and show commands, to gather relevant information without causing further disruptions to the network. Finally, outline the potential adjustments or optimizations you might propose to enhance the network’s EIGRP stability, convergence time, and scalability while minimizing.What specific connectivity issues are the network administrator experiencing? the impact on network traffic

They gave me 30 minutes to outline a answer.

We studied everything what they asked in CCNP Classes. Here is the summary

To diagnose and troubleshoot the intermittent connectivity issues in the network using EIGRP as the routing protocol, you can follow these steps:

  1. Analyze Topology Table: Check the EIGRP topology table on the routers to identify any inconsistencies or missing routes. Use the “show ip eigrp topology” command to view the contents of the topology table. Look for any routes marked as “inaccessible” or “active” and investigate further.
  2. Check Routing Table: Verify if the affected routes are present in the routing table of the routers using the “show ip route” command. Pay attention to the next-hop IP addresses, route metrics, and administrative distances. Ensure that the necessary routes are being advertised and installed correctly.
  3. Review Neighbor Relationships: Confirm that the neighbor relationships between the routers are established and functioning properly. Use the “show ip eigrp neighbors” command to check the status, uptime, and IP addresses of the neighboring routers. Look for any inconsistencies or dropped neighbor relationships.
  4. Consider Split-Horizon: Review the split-horizon feature, which prevents routing information from being sent back out of the interface it was received on. Make sure split-horizon is configured appropriately for each interface and take note of any exceptions or potential issues.
  5. Evaluate Feasible Successor Routes: Determine if there are feasible successor routes available for the affected destinations. Feasible successors act as backup routes that can be used to quickly restore connectivity if the primary route fails. Use the “show ip eigrp topology” command and analyze the reported successor and feasible successor routes.
  6. Verify EIGRP Metrics: Check the EIGRP metrics for the affected routes to ensure they are correctly calculated and reflect the desired path selection. Use the “show ip eigrp topology” command to view the reported delays, bandwidths, and reliability values associated with each route.
  7. Inspect Route Summarization: Examine if route summarization is implemented correctly in order to reduce the size of the routing table and optimize routing updates. Verify that summarized routes are being advertised and propagated consistently across the network.
  8. Consider Authentication: If authentication is enabled for EIGRP, verify that the authentication settings on all routers match. Ensure that keys or passwords are correctly configured and synchronized to avoid authentication failures.

To gather relevant information without causing disruptions, you can use debugging tools such as EIGRP packet captures and show commands:

  • Packet Captures: Use packet capture tools like Wireshark to capture EIGRP packets on specific interfaces or routers. Analyze these captures to identify any abnormalities, such as missing or malformed packets.
  • Show Commands: Utilize various show commands, such as “show ip eigrp interfaces,” “show ip eigrp topology,” and “show ip eigrp traffic,” to gather detailed information about EIGRP interfaces, neighbors, topology table entries, and traffic statistics.

Finally, to enhance the network’s EIGRP stability, convergence time, and scalability while minimizing disruptions, consider these adjustments or optimizations:

  • Tune EIGRP Metrics: Adjust the EIGRP metric values (such as bandwidth, delay, reliability) to optimize path selection based on network requirements. This can help improve performance and load balancing.
  • Implement Route Summarization: Configure appropriate route summarization to reduce the size of routing updates and improve network scalability.
  • Implement Equal-Cost Multipath (ECMP): Enable ECMP to utilize multiple equal-cost paths simultaneously, enhancing network resiliency, load balancing, and scalability.
  • Implement Fast Convergence Features: Enable features like EIGRP stub routing, EIGRP query optimization, and feasible successors to reduce convergence time and improve network stability.
  • Implement Network Redundancy: Implement redundant links or alternate paths between sites to provide additional fault tolerance and improve overall connectivity.

By following these steps and considering these adjustments, you can diagnose and troubleshoot connectivity issues in a network using EIGRP as the routing protocol while minimizing disruptions and optimizing its stability, convergence time, and scalability.