EIGRP (Enhanced Interior Gateway Routing Protocol)

What is EIGRP? — Enhanced Interior Gateway Routing Protocol

EIGRP (Enhanced Interior Gateway Routing Protocol) is an advanced distance-vector routing protocol developed by Cisco. It’s designed to provide fast convergence, scalability, and efficient routing inside large enterprise networks.

Key Features of EIGRP

Hybrid Protocol — Often called an advanced distance-vector or hybrid protocol because it combines the best of link-state and distance-vector approaches.

DUAL Algorithm — Uses the Diffusing Update Algorithm (DUAL) to ensure loop-free and backup routes quickly.

Fast Convergence — Reacts to network changes almost instantly.

Supports VLSM & CIDR — Fully classless, so it supports subnetting and efficient use of IP addresses.

Protocol Independence — Works with IPv4, IPv6, IPX, and AppleTalk (multiprotocol support).

Reduced Bandwidth Usage — Sends partial and bounded updates instead of flooding the entire routing table.

Load Balancing — Supports equal-cost and unequal-cost load balancing for optimized traffic flow.

EIGRP Metrics

EIGRP calculates the best path based on a composite metric of:

Bandwidth

Delay

Reliability

Load

MTU

(By default, bandwidth & delay are used.)

EIGRP Administrative Distances

Internal routes → 90

External routes → 170

Summary routes → 5

Lower values mean higher preference when compared to other protocols like OSPF (110) or RIP (120).

Why Use EIGRP?

Faster convergence than RIP

Easier to configure than OSPF

Efficient in large enterprise environments

Cisco-optimized (though now partly open standard)

EIGRP vs Other Protocols

RIP → More scalable, faster, and efficient.

OSPF → Easier to configure but slightly less scalable in multi-vendor setups.

BGP → EIGRP is for internal routing, while BGP is for inter-AS/global internet routing.

Final Thoughts

EIGRP is like a “smart GPS system” for enterprise networks — it not only finds the shortest path but also keeps backup routes ready in case of failure.

If you’re in networking or CCNA/CCNP studies, mastering EIGRP is a must for handling real-world Cisco-based infrastructures.

Pro tip: Always remember the EIGRP formula and DUAL concepts — they’ll help you shine in both interviews and practical labs!