🛰️ EIGRP (Enhanced Interior Gateway Routing Protocol)

 

🛰️ EIGRP (Enhanced Interior Gateway Routing Protocol)

🧠 Top 5 Key Points

  1. Hybrid Routing Protocol → Combines features of both distance vector and link-state protocols.

  2. Metric: Uses a composite metric (bandwidth, delay, reliability, load, MTU).

  3. Fast Convergence: Uses the DUAL algorithm (Diffusing Update Algorithm) for instant recovery and loop-free routes.

  4. Supports VLSM and CIDR → It’s classless, allowing subnet flexibility.

  5. Uses Autonomous System (AS) Numbers → All routers in the same EIGRP domain must share the same AS number.

⚙️ Technical Notes

  • Works at Layer 3 (Network Layer).

  • Cisco proprietary (though later open-standard EIGRP was introduced).

  • Uses multicast 224.0.0.10 for neighbor discovery.

🧰 EIGRP Lab in Cisco Packet Tracer

🎯 Goal:

Configure EIGRP between 3 routers so that all LANs can communicate.

🖥️ Network Topology

PC1 -- R1 -- R2 -- R3 -- PC2

IP Address Plan

DeviceInterfaceIP AddressNetwork
R1G0/0192.168.1.1192.168.1.0/24
S0/0/010.0.0.110.0.0.0/30
R2S0/0/010.0.0.210.0.0.0/30
S0/0/110.0.0.510.0.0.4/30
R3S0/0/110.0.0.610.0.0.4/30
G0/0192.168.2.1192.168.2.0/24
PC1NIC192.168.1.10192.168.1.0/24
PC2NIC192.168.2.10192.168.2.0/24

🪜 Step-by-Step Configuration

🔹 R1

enable
conf t
interface g0/0
 ip address 192.168.1.1 255.255.255.0
 no shutdown
exit
interface s0/0/0
 ip address 10.0.0.1 255.255.255.252
 clock rate 64000
 no shutdown
exit
router eigrp 100
 network 192.168.1.0
 network 10.0.0.0
 no auto-summary

🔹 R2

enable
conf t
interface s0/0/0
 ip address 10.0.0.2 255.255.255.252
 no shutdown
exit
interface s0/0/1
 ip address 10.0.0.5 255.255.255.252
 clock rate 64000
 no shutdown
exit
router eigrp 100
 network 10.0.0.0
 no auto-summary

🔹 R3

enable
conf t
interface s0/0/1
 ip address 10.0.0.6 255.255.255.252
 no shutdown
exit
interface g0/0
 ip address 192.168.2.1 255.255.255.0
 no shutdown
exit
router eigrp 100
 network 192.168.2.0
 network 10.0.0.0
 no auto-summary

🔍 Verification Commands

show ip eigrp neighbors

➡ Displays EIGRP neighbors.

show ip route eigrp

➡ Shows EIGRP-learned routes (marked with “D”).

show ip protocols

➡ Confirms EIGRP AS and networks in operation.

💡 Testing

  • Ping from PC1 to PC2:

    ping 192.168.2.10

✅ Successful replies = EIGRP routing working!

🧠 Key Learning Summary

ConceptDescription
EIGRP TypeAdvanced Distance Vector (Hybrid)
MetricBandwidth + Delay (Composite)
AlgorithmDUAL (Fast convergence)
Neighbor DiscoveryMulticast 224.0.0.10
AS NumberMust match on all routers

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