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Routing Information Protocol (RIP)

Definition

Routing Information Protocol (RIP) is a Distance Vector Routing Protocol that automatically exchanges routing information between routers. It determines the best path based on Hop Count and is designed for small networks.

Distance Vector Protocol Review

Definition

A Distance Vector (DV) routing protocol shares its entire routing table with directly connected neighbors at regular intervals.

Routers trust the routing information received from neighboring routers without independently verifying every route. This behavior is known as Routing by Rumor.

Key Points

  • Routers exchange their complete routing tables.
  • Updates are sent to directly connected neighbors.
  • Each router combines received routes with its own routing table.
  • The best route is selected based on the routing protocol’s metric.
  • If multiple routing protocols advertise the same destination, Administrative Distance (AD) determines which route is preferred.

Examples of Distance Vector Protocols

  • RIP (Routing Information Protocol)
  • IGRP (Interior Gateway Routing Protocol) (obsolete; no longer supported by Cisco)

RIP Characteristics

Definition

RIP is one of the oldest and simplest dynamic routing protocols.

Key Characteristics

  • Routing Protocol: RIP (Routing Information Protocol)
  • Routing Type: Distance Vector
  • Default Administrative Distance (AD): 120
  • Metric: Hop Count
  • Maximum Hop Count: 15
  • Hop 16: Destination is considered unreachable
  • Update Interval: Every 30 seconds
  • Best suited for small networks
  • Supports Equal-Cost Load Balancing
    • Default: 4 paths
    • Maximum: 6 equal-cost paths (platform dependent)

Hop Count

A Hop is one router crossed by a packet.

Example:

PC
 │
R1
 │
R2
 │
R3
 │
Server

Hop Count = 3

RIP always prefers the route with the fewest hops.

RIP Versions

There are three versions of RIP.

VersionIP VersionSupports VLSMRouting Type
RIPv1IPv4❌ NoClassful
RIPv2IPv4✅ YesClassless
RIPngIPv6✅ YesClassless

Neighbor Command

neighbor 192.168.20.2

Normally, RIP sends routing updates using broadcast (RIPv1) or multicast (RIPv2).

The neighbor command changes routing updates to unicast, sending updates only to the specified neighbor.

RIP Message Types

RIP uses two message types.

1. Request Message

Purpose:

  • Sent when a RIP-enabled interface starts.
  • Requests routing information from neighboring routers.

2. Response Message

Purpose:

  • Sent in reply to a Request message.
  • Contains the router’s routing table.

RIPv1

Definition

RIPv1 is the original version of RIP.

It is a Classful Distance Vector Routing Protocol, meaning it does not include subnet mask information in routing updates.

Characteristics

  • IPv4 only
  • Classful routing
  • No VLSM support
  • Uses Broadcast
  • No authentication
  • Hop Count metric
  • Maximum 15 hops

RIPv1 Configuration

Enable RIP

R1(config)# router rip

Starts the RIP routing process.

R1(config-router)# network 192.168.10.0
R1(config-router)# network 192.168.20.0
R1(config-router)# network 192.168.30.0
R1(config-router)# network 192.168.40.0

Each network command enables RIP on interfaces that belong to that network and advertises those networks to neighboring routers.

Display Routing Table

R1(config-router)# do show ip route

Displays the routing table without leaving configuration mode.

Passive Interface

R1(config-router)# passive-interface Serial2/0

Stops RIP updates from being sent out of the specified interface while still allowing the connected network to be advertised.

Neighbor Command

R1(config-router)# neighbor 192.168.20.2

Sends routing updates directly to the specified neighbor using unicast.

RIPv2

Definition

RIPv2 is an enhanced version of RIPv1.

It is a Classless Distance Vector Routing Protocol that supports modern IP addressing features such as VLSM and CIDR.

Characteristics

  • IPv4
  • Classless
  • Supports VLSM
  • Supports CIDR
  • Uses Multicast
  • Supports Authentication
  • Hop Count metric
  • Maximum 15 hops

RIPv1 vs RIPv2

FeatureRIPv1RIPv2
Routing TypeClassfulClassless
IPv4 SupportYesYes
Maximum Hop Count1515
AuthenticationNoMD5 or Plain Text
UpdatesBroadcastMulticast (224.0.0.9)
VLSM SupportNoYes
CIDR SupportNoYes
Administrative Distance120120

RIPv2 Configuration

Enable RIP

R1(config)# router rip

Starts the RIP routing process.

Enable Version 2

R1(config-router)# version 2

Enables RIPv2.

Disable Auto Summarization

R1(config-router)# no auto-summary

Disables automatic route summarization at classful network boundaries.

This is recommended when using VLSM or discontiguous networks.

R1(config-router)# network 192.168.10.0
R1(config-router)# network 192.168.20.0
R1(config-router)# network 192.168.30.0
R1(config-router)# network 192.168.40.0

Advertises the specified networks.

Advertising a Default Route Using RIP

A router can advertise a default route to all RIP neighbors.

Step 1: Configure the Default Route

Router(config)# ip route 0.0.0.0 0.0.0.0 14.0.0.4

This creates a static default route.

Step 2: Enable RIP

Router(config)# router rip

Starts the RIP routing process.

Step 3: Advertise the Default Route

Router(config-router)# default-information originate

This instructs RIP to advertise the configured default route to neighboring routers.

RIP Configuration Example

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)# network 192.168.2.0

Line-by-Line Explanation

CommandPurpose
router ripStarts RIP.
version 2Uses RIPv2.
no auto-summaryDisables automatic summarization.
network 192.168.1.0Advertises the first network.
network 192.168.2.0Advertises the second network.

RIP vs IGRP

Definition

Both RIP and IGRP are Distance Vector routing protocols.

However, IGRP was a Cisco proprietary protocol and is now obsolete.

Differences

RIPIGRP
Open standardCisco proprietary
Uses Hop CountUses Bandwidth, Delay, Reliability, and Load
Administrative Distance = 120Administrative Distance = 100
Maximum Hop Count = 15Maximum Hop Count = 255 (100 recommended)
No Autonomous System (AS) number requiredRouters must use the same Autonomous System (AS) number
Still supported (RIPv2)No longer supported by Cisco

Explanation

How RIP Works

  1. RIP is enabled on participating routers.
  2. Routers discover directly connected networks.
  3. Every 30 seconds, routers exchange routing tables with neighbors.
  4. Each router updates its routing table based on received information.
  5. Routes with the lowest hop count are selected.
  6. If multiple equal-cost routes exist, RIP performs load balancing.

Routing by Rumor

Distance Vector protocols do not maintain a complete map of the network.

Instead:

  • A router trusts information received from neighboring routers.
  • It assumes the neighbor’s information is correct.
  • Therefore, Distance Vector routing is often called Routing by Rumor.

Why RIPv2 Is Better Than RIPv1

  • Supports VLSM.
  • Supports CIDR.
  • Includes subnet masks in routing updates.
  • Supports authentication.
  • Uses multicast instead of broadcast, reducing unnecessary traffic.

Common Mistakes

  • Confusing Hop Count with Administrative Distance.
  • Forgetting that RIP cannot route beyond 15 hops.
  • Assuming RIPv1 supports VLSM—it does not.
  • Forgetting to configure version 2 when using RIPv2.
  • Forgetting no auto-summary in networks using VLSM or discontiguous addressing.
  • Thinking RIP is suitable for large enterprise networks; it is intended for small networks.
  • Confusing Broadcast (RIPv1) with Multicast (RIPv2) updates.

Short Exam Notes

  • RIP: Distance Vector routing protocol.
  • Metric: Hop Count.
  • Administrative Distance: 120.
  • Maximum Hop Count: 15 (16 = unreachable).
  • Routing Updates: Every 30 seconds.
  • RIPv1: Classful, Broadcast, No VLSM, No Authentication.
  • RIPv2: Classless, Multicast (224.0.0.9), Supports VLSM/CIDR, Supports Authentication.
  • RIPng: RIP for IPv6.
  • Passive Interface: Stops sending RIP updates on an interface while still advertising its network.
  • default-information originate: Advertises the default route through RIP.
  • IGRP: Cisco proprietary Distance Vector protocol, now obsolete.
  • Distance Vector: Exchanges complete routing tables with neighbors (“Routing by Rumor”).