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.
Feature
RIPv1
RIPv2
Addressing
Classful (A, B, C)
Classless (VLSM/CIDR)
Subnet Masks
Not sent in updates
Included in updates
Transmission
Broadcast (255.255.255.255)
Multicast (224.0.0.9)
Authentication
Not supported
Supported
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)
Term
Definition
Successor
The best, lowest-metric route installed in the routing table.
Feasible Successor (FS)
A loop-free backup route.
Feasible Distance (FD)
The local router's total metric to the destination.
Reported Distance (RD)
The metric advertised by a neighbor to reach the destination.
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
Command
Purpose
show ip protocols
Summarizes all active routing protocols (timers, AD, networks).
show ip route [rip | eigrp]
Filters the routing table for specific protocol entries.
show ip eigrp neighbors
Verifies successful adjacencies with neighboring routers.
show ip eigrp topology
Displays the DUAL database, including Successors and FS.
6.0 Head-to-Head Comparison: RIP vs. EIGRP
Feature
RIP
EIGRP
Type
Distance Vector
Advanced Distance Vector
Metric
Hop Count
Bandwidth + Delay
Convergence
Slow
Very Fast
Load Balancing
Equal Cost Only
Equal & Unequal Cost
Admin Distance
120
90
Standard
Industry Standard
Cisco (Open since 2013)