RIP – Distance Vector Protocol

Routing Information Protocol (RIP) – Distance Vector Protocol

Over the years, RIP has evolved from a classful routing protocol (RIPv1) to a classless routing protocol (RIPv2). RIPv2 is a standardised routing protocol that works in a mixed vendor router environment. Routers made by different companies can communicate using RIP. It is one of the easiest routing protocols to configure, making it a good choice for small networks. However, RIPv2 still has limitations. Both RIPv1 and RIPv2 have a route metric that is based only on hop count and that is limited to 15 hops. This really does limit RIP to quite small networks.

Features and characteristics of RIP include

■ Hop count is used as the metric for path selection.
■ If the hop count for a network is greater than 15, RIP cannot supply a route to that network.
■ Routing updates are broadcast or multicast every 30 seconds, by default.
■ Supports split horizon and split horizon with poison reverse to prevents loops.
■ Is capable of load-balancing up to six equal-cost paths. The default is four equal-cost paths.

RIPv2 introduced the following improvements to RIPv1:

■ Includes the subnet mask in the routing updates, making it a classless routing protocol
■ Has an authentication mechanism to secure routing table updates
■ Supports variable-length subnet mask (VLSM)
■ Uses multicast addresses instead of broadcast
■ Supports manual route summarisation

 Configuring RIP
Using the Cisco IOS, the command to enable RIP routing protocol is router rip. The version command is used to specify which RIP version to use (either 1 or 2). If the version command is omitted then the router defaults to sending RIPv1 but can receive both RIPv1 and RIPv2.

The network command is used to specify the directly connected subnets on the router to be configured and that are intended to be included in the routing updates. This is a good time to point out that you still specify classful networks with the network command.

According to the classful, network specified, the subnets of that network are automatically identified and participate in the routing update. By default routing updates are summarized at network boundaries.

In RIPv2 this auto summarisation behaviour can be turned off using the no auto-summary command. Moreover, manual summarization can be configured on a per interface level.

Example of use
Lets say you wanted to configure your router to use RIP version 2 to advertise two directly connected networks of 10.0.0.0/8 and 192.168.1.0/24 the following commands would be used.

Router(config)#router rip
Router(config-router)version 2
Router(config-router)network 10.0.0.0
Router(config-router)network 192.168.1.0

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