Introduction

Welcome back to Network ThinkTank, your go-to source for all things networking. In this post, we’ll delve into the Enhanced Interior Gateway Routing Protocol (EIGRP), a popular and robust routing protocol used in various networks around the globe. EIGRP is a Cisco proprietary protocol that combines the best of both distance-vector and link-state routing protocols to deliver an efficient, fast-converging, and highly scalable solution. Join us as we explore EIGRP’s core components and walk through an example configuration.

Key Components of EIGRP

1. Neighbor Discovery and Recovery

EIGRP routers discover and maintain neighbor relationships by exchanging Hello packets. Neighbors are adjacent routers that have compatible EIGRP configurations and share a common subnet. Once neighbors are discovered, routers exchange routing information and track each other’s status.

2. Reliable Transport Protocol (RTP)

EIGRP uses its own Reliable Transport Protocol (RTP) to ensure reliable and ordered delivery of EIGRP messages between neighbors. RTP tracks the status of sent messages and retransmits them if acknowledgements are not received within a specified time.

3. Diffusing Update Algorithm (DUAL)

EIGRP uses the Diffusing Update Algorithm (DUAL) to compute the shortest path and select backup paths, ensuring loop-free routing. DUAL monitors the network for changes and triggers EIGRP to quickly converge when topology changes occur.

4. Metrics

EIGRP calculates routes based on a composite metric that considers multiple factors, including bandwidth, delay, reliability, and load. This allows EIGRP to make more intelligent routing decisions compared to protocols that rely solely on hop count or link cost.

5. Route Summarization and Filtering

EIGRP supports route summarization and filtering to minimize the size of routing tables and control the propagation of routing information. This helps improve network scalability and efficiency.

Example Configuration

In this example, we will configure EIGRP on three routers (R1, R2, and R3) connected in a triangle topology.

R1 configuration:

router eigrp 100
network 10.0.0.0 0.0.0.255
network 192.168.1.0 0.0.0.255

R2 configuration:

router eigrp 100
network 10.0.0.0 0.0.0.255
network 10.0.1.0 0.0.0.255

R3 configuration:

router eigrp 100
network 10.0.1.0 0.0.0.255
network 192.168.1.0 0.0.0.255

In this configuration, EIGRP is enabled on each router with an autonomous system number (ASN) of 100. The ‘network’ command specifies the IP address ranges for EIGRP operation. R1 and R3 share the 192.168.1.0/24 network, while R1 and R2 share the 10.0.0.0/24 network, and R2 and R3 share the 10.0.1.0/24 network.

After configuring EIGRP, routers will exchange Hello packets to discover neighbors, share routing information, and use the DUAL algorithm to compute the shortest path and select backup paths.

Conclusion

EIGRP is a powerful routing protocol that combines the advantages of distance-vector and link-state protocols, offering an efficient and scalable solution for modern networks. As we continue to explore the world of networking, understanding EIGRP’s core components and