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EIGRP

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used in computer networks to automate routing decisions and configuration. Developed by Cisco, EIGRP is designed to offer superior internal routing capabilities within autonomous systems.

Overview of EIGRP​

  1. Advanced Distance-Vector Protocol: While EIGRP is classified as a distance-vector protocol, it incorporates features of link-state protocols, making it more efficient and faster in converging than traditional distance-vector protocols like RIP.

  2. Diffusing Update Algorithm (DUAL): EIGRP uses the DUAL algorithm to ensure loop-free and reliable routing. DUAL allows EIGRP to quickly adapt to network topology changes, providing rapid convergence.

  3. Protocol Independence: EIGRP is protocol-independent, supporting multiple network layer protocols such as IPv4, IPv6, IPX, and AppleTalk.

  4. Metric Calculation: EIGRP uses a composite metric based on bandwidth, delay, load, and reliability to determine the best path to a network destination.

  5. Efficient Use of Bandwidth: EIGRP sends partial updates only when the network topology changes, reducing the amount of bandwidth used for routing information.

  6. Route Summarization and Aggregation: EIGRP supports manual and automatic route summarization and aggregation, improving network efficiency and scalability.

How EIGRP Works​

  1. Neighbor Discovery and Formation: EIGRP routers discover each other and form neighbor relationships by sending "Hello" packets.

  2. Exchange of Routing Information: Once neighbors are established, routers exchange routing information. EIGRP keeps a copy of all neighbor's routing tables to have multiple paths to a destination.

  3. Best Path Selection: EIGRP uses the DUAL algorithm to select the best path to each destination network. The selected route is called the "successor", and backup routes are termed "feasible successors".

  4. Maintaining Routing Information: EIGRP maintains three tables:

    • Neighbor Table: Stores information about neighboring routers.
    • Topology Table: Contains routing information received from neighbors.
    • Routing Table: Holds the best routes to destination networks.

  5. Handling Topology Changes: If a route becomes unavailable, EIGRP queries its neighbors for an alternate path. If a feasible successor is available, it's used immediately, ensuring fast convergence.

Use Cases of EIGRP​

  1. Enterprise Networking: EIGRP is widely used in medium to large enterprise networks due to its scalability and flexibility.

  2. Rapid Convergence Requirements: In networks where rapid adaptation to topology changes is crucial, EIGRP's fast convergence is highly beneficial.

  3. Multi-Protocol Environments: EIGRP’s ability to support various network protocols makes it suitable for diverse network environments.

  4. Hierarchical Network Designs: Its support for route summarization and aggregation allows for efficient hierarchical network designs.

Conclusion​

EIGRP is a robust and efficient routing protocol ideal for modern network environments that require fast convergence, scalability, and support for multiple protocols. Its advanced features, combined with the ability to maintain multiple routes and efficiently utilize bandwidth, make it a popular choice for enterprise networks. However, it's important to note that EIGRP is a Cisco proprietary protocol, which may limit its implementation in non-Cisco environments, though there are versions of EIGRP that have been made available for use in multi-vendor environments.