How to Configure EIGRP on a Cisco Router: Step-by-Step Cisco IOS Guide If you need fast convergence, simple neighbor relationships, and efficient route exchange inside a Cisco-based network, EIGRP configuration on a Cisco router is still one of the most practical skills a network administrator can learn. Whether you are building a branch-office topology, a lab environment, or a production WAN edge, understanding how to configure EIGRP correctly can make your routing design more predictable and easier to troubleshoot. In this guide, we will walk through how to configure EIGRP on a Cisco router, explain the core Cisco IOS commands, verify neighbor formation, and review common mistakes that prevent routes from appearing in the routing table. Note: This article uses a straightforward lab example so you can adapt the same approach to real-world enterprise routing deployments. Why Use EIGRP on a Cisco Router? EIGRP, or Enhanced Interior Gateway Routing Protocol, is a dynamic routing protocol designed to exchange routes efficiently between routers. Unlike static routing, EIGRP allows routers to learn networks automatically, react to topology changes, and maintain routing intelligence without constant manual updates. Fast convergence: Routers react quickly when a path changes. Low administrative overhead: You do not have to define every remote route manually. Efficient route calculation: EIGRP uses metrics based on bandwidth and delay. Scalable design: It works well for campus, branch, and lab routing environments. Lab Topology for This EIGRP Configuration Example For this example, assume you have two Cisco routers connected together: R1 LAN: 192.168.10.0/24 R1-R2 link: 10.10.10.0/30 R2 LAN: 192.168.20.0/24 EIGRP AS number: 100 The goal is to advertise both LAN networks so each router learns the remote subnet dynamically through EIGRP. Step 1: Configure IP Addresses on Router Interfaces Before enabling EIGRP, make sure your router interfaces are addressed correctly and are in an up state. Here is a sample configuration for R1: enable configure terminal interface GigabitEthernet0/0 ip address 192.168.10.1 255.255.255.0 no shutdown exit interface GigabitEthernet0/1 ip address 10.10.10.1 255.255.255.252 no shutdown exit And here is a sample configuration for R2: enable configure terminal interface GigabitEthernet0/0 ip address 192.168.20.1 255.255.255.0 no shutdown exit interface GigabitEthernet0/1 ip address 10.10.10.2 255.255.255.252 no shutdown exit At this stage, the directly connected interfaces should be reachable. You can validate local interface status with: show ip interface brief Step 2: Enable EIGRP on the Cisco Router Once interface addressing is complete, enable EIGRP using the same autonomous system number on both routers. In this example, we use 100. On R1: router eigrp 100 network 192.168.10.0 0.0.0.255 network 10.10.10.0 0.0.0.3 no auto-summary On R2: router eigrp 100 network 192.168.20.0 0.0.0.255 network 10.10.10.0 0.0.0.3 no auto-summary The network statements tell the router which interfaces should participate in EIGRP. The no auto-summary command is important in modern routed environments because it prevents classful route summarization that can create inaccurate routing behavior. Step 3: Verify EIGRP Neighbor Adjacency After EIGRP is enabled, the routers should discover each other across the 10.10.10.0/30 link. One of the first verification commands every network admin should run is: show ip eigrp neighbors If the configuration is correct, each router should list the other router as an EIGRP neighbor. This confirms that the adjacency is formed and route exchange can begin. If you do not see a neighbor, check these items: The interfaces are not shut down. The routers are in the same IP subnet on the transit link. The EIGRP AS number matches on both routers. The transit interface is included in the EIGRP network command. Step 4: Confirm Learned Routes in the Routing Table Once adjacency is established, each router should install the remote LAN as an EIGRP-learned route. Use this command: show ip route eigrp For example, on R1 you should see the 192.168.20.0/24 network learned through R2. On R2 you should see the 192.168.10.0/24 network learned through R1. You can also inspect the EIGRP topology table with: show ip eigrp topology This command is useful when you want deeper visibility into successor routes, feasible successors, and path selection logic. Step 5: Use Passive Interfaces for Better Routing Hygiene In a production network, you often do not want EIGRP hello packets sent toward end-user LAN segments. A cleaner design is to make non-router-facing interfaces passive while still advertising the connected subnet. Example on R1: router eigrp 100 passive-interface GigabitEthernet0/0 no passive-interface GigabitEthernet0/1 This allows the LAN network to remain advertised while preventing unnecessary neighbor formation attempts on the user-facing interface. Step 6: Save the Cisco Router Configuration After verifying that EIGRP is working, save the running configuration so the router retains it after a reboot: write memory Or, if you prefer the longer form: copy running-config startup-config Useful Show Commands for EIGRP Troubleshooting When troubleshooting Cisco router EIGRP configuration, these commands are worth memorizing: show ip interface brief — confirms interface addressing and status. show ip protocols — displays active routing protocols and EIGRP network statements. show ip eigrp neighbors — checks whether adjacencies are formed. show ip route eigrp — shows routes learned through EIGRP. show ip eigrp topology — displays EIGRP path information. Common EIGRP Configuration Mistakes on Cisco IOS Even a simple EIGRP deployment can fail if one small setting is off. Here are some of the most common issues: Mismatched AS numbers: Both routers must use the same EIGRP autonomous system number. Wrong wildcard mask: A bad wildcard mask can prevent the interface from joining EIGRP. Missing transit network: If the inter-router link is not advertised, no adjacency will form. Shutdown interface: EIGRP cannot operate on an interface that is administratively down. Layer 3 connectivity problems: IP addressing errors break neighbor formation before routing even starts. Complete Example Configuration Here is a clean end-to-end example you can use in a Cisco lab: ! R1 enable configure terminal hostname R1 interface GigabitEthernet0/0 ip address 192.168.10.1 255.255.255.0 no shutdown exit interface GigabitEthernet0/1 ip address 10.10.10.1 255.255.255.252 no shutdown exit router eigrp 100 network 192.168.10.0 0.0.0.255 network 10.10.10.0 0.0.0.3 passive-interface GigabitEthernet0/0 no auto-summary end write memory ! R2 enable configure terminal hostname R2 interface GigabitEthernet0/0 ip address 192.168.20.1 255.255.255.0 no shutdown exit interface GigabitEthernet0/1 ip address 10.10.10.2 255.255.255.252 no shutdown exit router eigrp 100 network 192.168.20.0 0.0.0.255 network 10.10.10.0 0.0.0.3 passive-interface GigabitEthernet0/0 no auto-summary end write memory Final Thoughts on Configuring EIGRP on a Cisco Router Learning how to configure EIGRP on a Cisco router gives you a solid foundation in dynamic routing and Cisco IOS operations. Once the interfaces are addressed, the EIGRP process is enabled, and the correct networks are advertised, the protocol handles route sharing automatically and efficiently. For most administrators, the real value comes from knowing how to verify the neighbor relationship and quickly troubleshoot common errors. If you can read show ip eigrp neighbors, show ip route eigrp, and show ip protocols with confidence, you will solve most EIGRP issues much faster in both lab and production environments.