Routing Information Protocol (RIP)

The Routing Information Protocol (RIP) is designed to help routers determine the best path for sending data packets across a network. It uses hop count as its routing metric and is primarily used in small to medium-sized networks due to its scalability limitations.

• RIP operates at the Network Layer (Layer 3) of the OSI model and maintains routing tables on each router.
• Every 30 seconds, routers exchange their complete routing tables with neighbours using periodic updates.
• The hop count metric defines the number of routers a packet must pass through to reach its destination.

Note: RIP supports a maximum hop count of 15, which limits its use in larger networks. A hop count of 16 is considered unreachable.

Hop Count

Hop count is a routing metric that represents the total number of routers a data packet must pass through to travel from the source device to the destination device.

• Each router crossed by a packet is counted as one hop.
• Used by routing protocols like RIP to determine the best path.
• RIP selects the route with the lowest hop count as the optimal route.
• The maximum hop count in RIP is 15; a hop count of 16 is considered unreachable.
• Limiting the hop count helps prevent routing loops.
• This limitation reduces RIP’s scalability, making it unsuitable for large networks.

Features of RIP

• Exchanges updates periodically (every 30 seconds).
• Broadcasts (RIPv1) or multicasts (RIPv2/RIPng) routing information.
• Sends entire routing tables in updates.
• Works on the principle of routing by rumour (trusting neighbours’ information).
• Uses route poisoning and split horizon to avoid routing loops.

How RIP Works

Routing Information Protocol (RIP) is a distance-vector routing protocol that determines the best path to a destination network based on hop count.

• Each router maintains a routing table containing distances to all known networks.
• Routers periodically exchange routing information with neighboring routers.
• Every 30 seconds, routers broadcast or multicast their entire routing table.
• If a router learns a shorter path, it updates its routing table accordingly.
• If a route is not updated within 180 seconds, it is marked as invalid.
• If the route remains unused for 240 seconds, it is removed (flushed) from the routing table.
• These timers help maintain accurate routing information and prevent stale routes.

Types of RIP Versions

RIP Timers

• Update Timer: Default 30 seconds (interval between updates).
• Invalid Timer: 180 seconds (route not updated = marked invalid).
• Hold-down Timer: 180 seconds (time to suppress unstable routes).
• Flush Timer: 240 seconds (time before removing invalid routes).

Note: Adjustable using the timers basic command.

RIP Configuration Example

Consider three routers (R1, R2, R3) connected in a network. Configuration on each router:

For R1

R2(config)# router rip
R2(config-router)# version 2
R2(config-router)# no auto-summary
R2(config-router)# network 192.168.10.0
R2(config-router)# network 172.16.10.0

For R2

R2(config)# router rip
R2(config-router)# version 2
R2(config-router)# no auto-summary
R2(config-router)# network 192.168.10.0
R2(config-router)# network 172.16.10.0

For R3

R3(config)# router rip
R3(config-router)# version 2
R3(config-router)# no auto-summary
R3(config-router)# network 10.10.10.0
R3(config-router)# network 172.16.10.0
R3(config-router)# network 172.16.10.4

Useful Commands

• debug ip rip -> Monitor RIP updates in real time.
• show ip route -> Display the routing table.
• show ip protocols -> Display routing protocols in use.

Where is RIP Used?

• Small to medium-sized networks with simple routing needs.
• Legacy networks that were built before OSPF/EIGRP became standard.
• Educational labs for training and learning routing basics.
• Backup routing protocol in case the primary protocol fails.