CCNA

Configuring EIGRP on a Cisco Router

Jay

09 Jul 2009 • 2 min read

What is EIGRP?

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol that combines the best features of distance vector and link-state protocols. EIGRP uses the Diffusing Update Algorithm (DUAL) to ensure loop-free routing and provides fast convergence times.

Basic EIGRP Configuration

To configure EIGRP on a Cisco router, follow these basic steps:

Step 1: Enter Global Configuration Mode

Router> enable
Router# configure terminal

Step 2: Enable EIGRP Process

Router(config)# router eigrp 100

The number 100 is the Autonomous System (AS) number. All routers in the same EIGRP domain must use the same AS number.

Step 3: Configure Network Statements

Router(config-router)# network 192.168.1.0
Router(config-router)# network 10.0.0.0

The network command tells EIGRP which interfaces to include in the routing process. EIGRP will advertise these networks and form adjacencies on interfaces that fall within these network ranges.

Advanced EIGRP Configuration

Wildcard Masks

You can use wildcard masks for more precise network specification:

Router(config-router)# network 192.168.1.0 0.0.0.255

Passive Interfaces

To prevent EIGRP from sending hello packets on specific interfaces:

Router(config-router)# passive-interface GigabitEthernet0/1

Auto-Summary

By default, EIGRP performs automatic summarization. To disable it:

Router(config-router)# no auto-summary

EIGRP Verification Commands

View EIGRP Neighbors

Router# show ip eigrp neighbors

View EIGRP Topology Table

Router# show ip eigrp topology

View EIGRP Interfaces

Router# show ip eigrp interfaces

View Routing Table

Router# show ip route eigrp

Example Configuration

Here's a complete example of EIGRP configuration on a router with multiple interfaces:

Router> enable
Router# configure terminal
Router(config)# router eigrp 100
Router(config-router)# network 192.168.1.0 0.0.0.255
Router(config-router)# network 192.168.2.0 0.0.0.255
Router(config-router)# network 10.0.0.0 0.0.0.255
Router(config-router)# no auto-summary
Router(config-router)# passive-interface GigabitEthernet0/2
Router(config-router)# exit
Router(config)# exit

Key EIGRP Concepts

Autonomous System (AS): All EIGRP routers must share the same AS number to exchange routes
Feasible Distance (FD): The best metric to reach a destination network
Advertised Distance (AD): The metric reported by a neighboring router
Successor: The primary route to a destination
Feasible Successor: A backup route that meets the feasibility condition

Troubleshooting EIGRP

Common EIGRP issues and solutions:

Neighbors not forming: Check AS numbers, network statements, and interface status
Routes not appearing: Verify network statements and ensure no auto-summary if needed
Suboptimal routing: Check metric calculations and bandwidth settings

Use debug commands for detailed troubleshooting:

Router# debug eigrp packets
Router# debug eigrp neighbors

Remember to disable debugging when finished:

Router# no debug all

EIGRP is a powerful and efficient routing protocol that's essential for CCNA candidates to understand. Practice these configurations in a lab environment to gain hands-on experience with EIGRP deployment and troubleshooting.