Day 25: RIP and EIGRP Routing Protocols

CCNA Study Guide: Comparative Analysis of RIP and EIGRP

1.0 Introduction

While OSPFv2 is the primary protocol for configuration on the CCNA 200-301 exam, understanding RIP and EIGRP is essential for mastering routing fundamentals. These protocols represent the evolution of distance-vector logic and provide context for why modern networks are designed the way they are.

2.0 Routing Information Protocol (RIP)

RIP is the classic "Routing by Rumor" protocol. It is a legacy Interior Gateway Protocol (IGP) that relies on periodic updates and a simplistic view of the network.

2.1 Core Characteristics

• Algorithm: Bellman-Ford (Distance Vector).

• Metric: Hop Count. Each router is one hop; the path with the fewest routers is chosen.

• Maximum Hop Count: 15. A hop count of 16 is considered "infinite" (unreachable).

• Administrative Distance (AD): 120.

• Update Timer: Full routing table broadcast/multicast every 30 seconds.

2.2 Evolution: RIPv1 vs. RIPv2

RIP evolved to support modern networking requirements like VLSM and CIDR.

2.3 Basic Configuration

Router(config)# router rip

Router(config-router)# version 2

Router(config-router)# no auto-summary

Router(config-router)# network 192.168.1.0

Router(config-router)# passive-interface g0/0

Router(config-router)# default-information originate

3.0 Enhanced Interior Gateway Routing Protocol (EIGRP)

EIGRP is an Advanced Distance Vector (or Hybrid) protocol. It is designed for extremely fast convergence and efficiency, utilizing the Diffusing Update Algorithm (DUAL).

3.1 Core Characteristics

• Algorithm: DUAL.

• Multicast Address: 224.0.0.10.

• Administrative Distance (AD): 90 (Internal), 170 (External).

• Convergence: Very fast due to pre-calculated backup paths.

• Routing Code: Identified in the routing table by the letter D (for DUAL).

3.2 The Composite Metric

EIGRP uses a complex formula considering multiple path attributes. By default, only Bandwidth and Delay are used.

$$Metric = ([Slowest\ Bandwidth + Sum\ of\ Delays] \times 256)$$

3.3 EIGRP Terminology (DUAL)

The Feasibility Condition: For a neighbor to be a Feasible Successor, its RD must be less than the current FD ($RD < FD$). This ensures a loop-free backup path.

4.0 Advanced Features and Configuration

4.1 Unequal-Cost Load Balancing

EIGRP is the only IGP that supports unequal-cost load balancing. Using the variance command, a router can distribute traffic across paths with different metrics if the backup path is a Feasible Successor.

4.2 Configuration Example

Router(config)# router eigrp 100

Router(config-router)# eigrp router-id 1.1.1.1

Router(config-router)# network 10.0.0.0 0.0.0.255

Router(config-router)# no auto-summary

Router(config-router)# variance 2

5.0 Verification and Troubleshooting Commands

6.0 Head-to-Head Comparison: RIP vs. EIGRP