🎯 Lab Objectives
- Understand EIGRP's hybrid nature (distance-vector + link-state features)
- Configure EIGRP with autonomous system numbers
- Verify neighbour adjacencies and routing table entries
- Understand the composite metric (bandwidth + delay)
- Configure passive interfaces on LAN-facing ports
Step 1 — EIGRP Overview
| Feature | Value |
|---|
| Type | Advanced distance-vector (Cisco proprietary) |
| Algorithm | DUAL (Diffusing Update Algorithm) |
| Metric | Composite (bandwidth + delay by default) |
| AD (internal) | 90 |
| AD (external) | 170 |
| Transport | IP Protocol 88 (not TCP/UDP) |
| Hello interval | 5s (LAN) / 60s (WAN) |
| Hold timer | 3x Hello (15s / 180s) |
| Multicast | 224.0.0.10 |
Step 2 — Lab Topology
.1 .2
R1 ---[Gi0/1]-------[Gi0/1]--- R2
10.0.12.0/30 10.0.23.0/30
.1 .2
R2 ---[Gi0/2]-------[Gi0/2]--- R3
LANs:
R1: 192.168.1.0/24 (Gi0/0)
R3: 192.168.3.0/24 (Gi0/0)
EIGRP AS: 100
Step 3 — Basic EIGRP Configuration
! R1
router eigrp 100
network 10.0.12.0 0.0.0.3
network 192.168.1.0
no auto-summary
! R2
router eigrp 100
network 10.0.12.0 0.0.0.3
network 10.0.23.0 0.0.0.3
no auto-summary
! R3
router eigrp 100
network 10.0.23.0 0.0.0.3
network 192.168.3.0
no auto-summary
# no auto-summary is CRITICAL in modern IOS
# Without it, EIGRP summarises to classful boundaries which breaks routing
Step 4 — Wildcard Masks
# EIGRP network statements use wildcard masks (inverse of subnet mask)
# /30 subnet mask: 255.255.255.252
# Wildcard: 0.0.0.3
# /24 subnet mask: 255.255.255.0
# Wildcard: 0.0.0.255
# /16 subnet mask: 255.255.0.0
# Wildcard: 0.0.255.255
# To advertise all interfaces in EIGRP (any IP):
router eigrp 100
network 0.0.0.0 255.255.255.255
Step 5 — Verify Neighbours
# Show EIGRP neighbours
show ip eigrp neighbors
# Expected output on R2:
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
0 10.0.12.1 Gi0/1 14 00:05:12 10 200 0 15
1 10.0.23.2 Gi0/2 12 00:05:10 11 200 0 12
# Show EIGRP routes (D = EIGRP)
show ip route eigrp
# Show EIGRP topology table
show ip eigrp topology
# Topology shows:
# Successor → best path (in routing table)
# Feasible Successor → backup path (instant failover, no recompute)
Step 6 — EIGRP Metric
# EIGRP composite metric formula (default: BW + Delay)
# Metric = 256 * (10^7/min_BW + sum_delay/10)
#
# min_BW = minimum bandwidth along the path (Kbps)
# sum_delay = cumulative delay along the path (microseconds)
# Default bandwidth values:
# Serial (T1) = 1544 Kbps
# FastEthernet = 100,000 Kbps
# GigabitEthernet = 1,000,000 Kbps
# Modify bandwidth on interface (affects metric, not actual speed)
interface GigabitEthernet0/1
bandwidth 512 # in Kbps
# Modify delay
interface GigabitEthernet0/1
delay 100 # in tens of microseconds
Step 7 — Passive Interfaces
# Stop sending EIGRP Hellos on LAN interfaces
router eigrp 100
passive-interface GigabitEthernet0/0 # LAN toward PCs
# Set all passive, then enable only on router-facing links
router eigrp 100
passive-interface default
no passive-interface GigabitEthernet0/1 # to R2
Step 8 — Troubleshooting
# Neighbours not forming? Check:
# 1. Same AS number on both routers?
# 2. K-values match? (must be identical)
# 3. Same subnet?
# 4. Authentication mismatch?
# Check K-values
show ip protocols | section eigrp
# Debug EIGRP
debug eigrp packets
debug ip eigrp
undebug all
# Verify routing table has EIGRP routes
show ip route | include D
📋 EIGRP Command Reference
| Command | Purpose |
|---|
router eigrp 100 | Enable EIGRP AS 100 |
network x.x.x.x w.w.w.w | Advertise network |
no auto-summary | Disable auto-summarisation |
show ip eigrp neighbors | View neighbours |
show ip eigrp topology | View topology table (successor/FS) |
show ip route eigrp | EIGRP routes in routing table |
show ip protocols | EIGRP K-values and settings |
✅Lab Complete! EIGRP is Cisco proprietary but still common in enterprise networks. The Feasible Successor concept gives it faster convergence than most routing protocols.