Enhanced Interior Gateway Routing Protocol (EIGRP) has established itself as a robust and scalable routing protocol for many enterprise environments. Introduced by Cisco as a hybrid distance-vector protocol, EIGRP offers fast convergence, loop-free operation, and support for VLSM and CIDR.
In this post, we walk through a multi-area topology configuration using EIGRP, focusing on summarization, route filtering, and metrics tuning. This setup helps network engineers design resilient and optimized routing domains.
Network Design Overview
Let’s consider a scenario with three routing domains: Core, Distribution, and Access. Each domain consists of multiple routers, and we aim to build EIGRP neighbor relationships across them while keeping the topology scalable and manageable.
Core Distribution Access
[R1]────[R2]────[R3]────[R4]────[R5]
Each router represents a different area in our logical hierarchy, though EIGRP does not support traditional areas like OSPF. Instead, we will use route summarization and stub routing to emulate area-like behavior and keep routing tables concise.
Step-by-Step EIGRP Configuration
1. Enable EIGRP on All Interfaces
R1(config)# router eigrp 100
R1(config-router)# network 10.0.0.0 0.255.255.255
Ensure all participating routers use the same autonomous system number (AS). This allows neighbor adjacencies to form.
2. Use Wildcard Masks for Precision
R2(config)# router eigrp 100
R2(config-router)# network 10.1.1.0 0.0.0.255
R2(config-router)# network 10.1.2.0 0.0.0.255
Applying more specific wildcard masks helps control which interfaces participate in EIGRP.
3. Configure Passive Interfaces Where Needed
R3(config-router)# passive-interface default
R3(config-router)# no passive-interface FastEthernet0/0
We prevent EIGRP updates from being sent on interfaces that don’t need to form adjacencies, enhancing security and efficiency.
4. Implement Route Summarization
R4(config-router)# interface FastEthernet0/1
R4(config-if)# ip summary-address eigrp 100 10.1.0.0 255.255.0.0
Route summarization reduces the size of routing tables and suppresses unnecessary route flaps.
5. Configure Stub Routing at the Edge
R5(config-router)# eigrp stub connected summary
Stub routers prevent transit traffic and keep routing protocol overhead minimal on access routers.
Tuning Metrics and Convergence
Adjusting delay and bandwidth parameters on interfaces helps influence EIGRP path selection.
R2(config-if)# interface FastEthernet0/0
R2(config-if)# bandwidth 1000
R2(config-if)# delay 10
Remember: EIGRP uses bandwidth, delay, reliability, and load to calculate its composite metric (K values default: K1=1, K3=1).
Verifying the Configuration
R3# show ip eigrp neighbors
R3# show ip route eigrp
R3# show ip protocols
Use these commands to check neighbor relationships, routing table entries, and protocol timers.
Conclusion
Deploying EIGRP in a segmented network demands careful attention to summarization, filtering, and interface tuning. By adopting stub routers and thoughtful route advertisement policies, engineers can maintain fast convergence and efficient routing in medium to large topologies.