Hands-On Lab: Configuring Basic EIGRP Routing

Lab Objective

Configure EIGRP with a common autonomous system number on three routers, verify neighbor adjacencies form, and confirm each router learns routes to networks it is not directly connected to.

Lab Purpose

Basic EIGRP configuration establishes the foundational workflow that every more advanced EIGRP topic builds upon — matching AS numbers between routers is the single most critical requirement, since a mismatch silently prevents any neighbor relationship from forming at all.

Lab Topology

R1 ---- Serial0/0/0 ---- R2 ---- Serial0/0/1 ---- R3

R1: 10.10.10.1/30, LAN 192.168.10.0/24
R2: 10.10.10.2/30 and 10.20.20.1/30
R3: 10.20.20.2/30, LAN 192.168.30.0/24

EIGRP AS 100 to be used throughout

Task 1: Configure Basic Addressing

Configure all interfaces shown, including each router's LAN.

Task 2: Enable EIGRP on All Three Routers

Enable EIGRP AS 100 on all three routers, advertising the appropriate networks.

Task 3: Verify Neighbor Formation

Confirm EIGRP neighbor relationships form between R1-R2 and R2-R3.

Task 4: Verify Routes Are Learned

Confirm R1 has learned about R3's LAN via EIGRP, despite no direct connection.

Task 5: Verify End-to-End Connectivity

Confirm R1's LAN can reach R3's LAN.

Solution and Verification

R1(config)# interface serial0/0/0
R1(config-if)# ip address 10.10.10.1 255.255.255.252
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface gigabitethernet0/0
R1(config-if)# ip address 192.168.10.1 255.255.255.0
R1(config-if)# no shutdown

R2(config)# interface serial0/0/0
R2(config-if)# ip address 10.10.10.2 255.255.255.252
R2(config-if)# clock rate 64000
R2(config-if)# no shutdown
R2(config-if)# exit
R2(config)# interface serial0/0/1
R2(config-if)# ip address 10.20.20.1 255.255.255.252
R2(config-if)# clock rate 64000
R2(config-if)# no shutdown

R3(config)# interface serial0/0/1
R3(config-if)# ip address 10.20.20.2 255.255.255.252
R3(config-if)# no shutdown
R3(config-if)# exit
R3(config)# interface gigabitethernet0/0
R3(config-if)# ip address 192.168.30.1 255.255.255.0
R3(config-if)# no shutdown

R1(config)# router eigrp 100
R1(config-router)# network 10.10.10.0 0.0.0.3
R1(config-router)# network 192.168.10.0
R1(config-router)# no auto-summary

R2(config)# router eigrp 100
R2(config-router)# network 10.10.10.0 0.0.0.3
R2(config-router)# network 10.20.20.0 0.0.0.3
R2(config-router)# no auto-summary

R3(config)# router eigrp 100
R3(config-router)# network 10.20.20.0 0.0.0.3
R3(config-router)# network 192.168.30.0
R3(config-router)# no auto-summary

R1# show ip eigrp neighbors

H   Address         Interface   Hold Uptime
0   10.10.10.2      Se0/0/0      13  00:02:14

R1# show ip route eigrp

D    10.20.20.0/30 [90/2681856] via 10.10.10.2, Serial0/0/0
D    192.168.30.0/24 [90/2707456] via 10.10.10.2, Serial0/0/0

R1# ping 192.168.30.1

!!!!!
Success rate is 100 percent (5/5)

Key Takeaway

The AS number in router eigrp 100 must match exactly between every router expected to form a neighbor relationship — unlike OSPF's process ID which is only locally significant, this value is exchanged and checked during EIGRP neighbor formation, making a typo here a common and easy-to-miss cause of neighbors that simply never appear.