EIGRP Routing Lab

        .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

! 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

# 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

# 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)

# 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

# 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

# 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