Configuring EIGRP on Cisco Routers: A Step-by-Step Guide

Configuring Enhanced Interior Gateway Routing Protocol (EIGRP) on Cisco routers involves several steps. EIGRP is a Cisco-proprietary routing protocol designed for routing within an Autonomous System (AS). Here’s a basic outline of how to configure EIGRP on Cisco routers:

1. Access the Router: Connect to the router using a terminal emulator program like PuTTY or a console cable. You can use the console port or SSH/TELNET, depending on your network setup.
2. Access Configuration Mode: Log in to the router and access privileged exec mode by typing:
   enable


   Then, access global configuration mode by typing:

   configure terminal

3. Enable EIGRP: To enable EIGRP, use the following command:
   router eigrp [AS_NUMBER]


   Replace [AS_NUMBER] with the Autonomous System Number you want to use for EIGRP. All routers in the same EIGRP domain (AS) should use the same AS number.

4. Define EIGRP Network Interfaces: You need to specify which interfaces will participate in EIGRP. Use the following command for each interface:
   network [NETWORK_ADDRESS] [WILDCARD_MASK]


   Replace [NETWORK_ADDRESS] with the IP network address and [WILDCARD_MASK] with the wildcard mask. This command tells the router which networks are part of the EIGRP process.

5. Optionally, Set Passive Interfaces: To prevent EIGRP from sending hello packets and updates on specific interfaces, you can mark them as passive. This is useful for interfaces that don’t connect to other EIGRP routers. Use the following command for each passive interface:
   passive-interface [INTERFACE_NAME]

6. Set EIGRP Metrics (Optional): By default, EIGRP uses bandwidth and delay to calculate metrics. If you want to adjust the metrics manually, you can use the following command under the EIGRP routing process:
   metric weights [K1] [K2] [K3] [K4] [K5]


   The values K1 to K5 are the multipliers for different metrics. The default values are 1 for bandwidth and delay and 0 for all others.

7. Configure Authentication (Optional): You can configure authentication for EIGRP using the following commands:
   ip authentication mode eigrp [AS_NUMBER] md5
ip authentication key-chain eigrp [AS_NUMBER] [KEY_CHAIN_NAME]


   This ensures that EIGRP updates are authenticated using a Message Digest 5 (MD5) key chain.

8. Exit Configuration Mode: When you’ve completed the EIGRP configuration, exit the configuration mode by typing:
   end

9. Save Configuration: To save your configuration, type:
   write memory


   This ensures that your EIGRP configuration persists through router reboots.

10. Verify and Monitor: Use the following commands to verify EIGRP configurations and monitor the routing process:

These commands will show information about EIGRP neighbor relationships, the routing table, and EIGRP interfaces.

Remember that EIGRP configurations should be consistent across routers within the same AS for proper routing. Additionally, make sure that the interfaces specified in the network statements are correctly configured with IP addresses and are in the “up” state.

Now, we can have also some other additional and advanced configurations for EIGRP.

11. Load Balancing: By default, EIGRP supports load balancing across equal-cost paths. You can control the load-balancing behavior with the variance command under the EIGRP process. For example, to load balance across paths with metrics up to two times the minimum metric, you can use:
    variance 2

12. Summarization: EIGRP allows you to summarize routes to reduce the size of the routing table. You can configure route summarization at the interface level with the following command:
    ip summary-address eigrp [AS_NUMBER] [NETWORK_ADDRESS] [SUBNET_MASK]


    This command summarizes routes at the specified interface, and the summarized route will be advertised into the EIGRP domain.

13. Route Filtering: You can filter routes with access lists when redistributing routes into or out of EIGRP. For example, if you want to filter routes when redistributing from OSPF into EIGRP, you can use:
    distribute-list [ACCESS_LIST_NAME] out [INTERFACE_NAME]

14. Stub Routers: EIGRP supports stub routers, which are routers that don’t need to know about all routes in the network. You can configure a router as a stub router with the following command:
    eigrp stub [CONNECTED | STATIC | SUMMARY | REDISTRIBUTE | LEAK-MAP]


    This helps reduce the query overhead on stub routers and simplifies configuration.

15. Route Tagging: You can tag EIGRP routes for better route control and filtering. To tag a route with a value, use:
    redistribute [SOURCE_PROTOCOL] [ROUTE_MAP_NAME] route-map-tag


    Then, you can match and filter routes based on tags using route maps.

16. EIGRP Timers: You can adjust various EIGRP timers to fine-tune convergence and stability. Key EIGRP timers include the “hello” interval and the “hold” timer. For example, to change the hello interval:
    ip hello-interval eigrp [AS_NUMBER] [INTERFACE_NAME] [HELLO_INTERVAL]

17. Monitoring and Troubleshooting: Use the following commands for monitoring and troubleshooting EIGRP:

• show ip eigrp topology: Displays the EIGRP topology table.
• debug eigrp packets: Enables packet-level debugging for EIGRP. Use with caution in a production network.
• clear ip eigrp [AS_NUMBER] neighbors: Clears EIGRP neighbor relationships.

18. Route Redistribution: If you need to redistribute routes from another routing protocol into EIGRP or vice versa, use the redistribute command within the EIGRP process.
19. BGP Peering (For EIGRP to BGP Integration): If you want to integrate EIGRP with BGP, you can peer the EIGRP router with a BGP router. This allows you to exchange routes between the two routing protocols. Use the neighbor command within the BGP process to establish the BGP peering.
20. Document Your Configuration: Do not forget maybe the most important part after you finish the configuration. Proper documentation is crucial for managing your network. Document your EIGRP configuration, including the AS number, network statements, summarization, and any special considerations.

Remember to thoroughly test any changes to your network configuration in a lab or non-production environment before applying them in a production network. This helps prevent unintended disruptions to your network.