Routing Information Protocol - RIP

Introduction

Routing Information Protocol (RIP) is a true Distance-Vector routing protocol. It sends the complete routing table out to all active interfaces every 30 seconds. RIP only uses hop count to determine the best way to a remote network, but it has a maximum allowable hop count of 15, meaning that 16 is deemed unreachable. RIP works well in small networks, but it is inefficient on large networks with slow WAN links or on networks with large number of routers installed.

RIP comes in two different versions. RIP version 1 uses only classful routing, which means that all devices in the network must use the same subnet mask. This is because RIP version 1 does not include the subnet mask when it sends updates. RIP v1 uses broadcasts (255.255.255.255).

RIP version 2 does, however, and this is what we call classless routing (check the Subnetting section for more details). RIP v2 uses multicasts (224.0.0.9) to update its routing tables.

Route Update Timer: Sets the interval, usually 30 seconds, between periodic routing updates, in which the router sends a complete copy of its routing table out to all neighbor routers.

Route Invalid Timer: Determines the length of time that must expire, usually 90 seconds, before the router determines that a route is invalid. It will come to this conclusion if it doesn't hear any updates about that route for that period. When the timer expires, the router will send out an update to its neighbors letting them know that the route is invalid.

Route Flush Timer: Sets the time between a route becoming invalid and its removal from the routing table (240 secs). Before it's removed, the router will notify its neighbors of that route's impending doom ! The value of the route invalid timer must be less than that of the route flush timer. This is to provide the router with enough time to tell its neighbors about the invalid route before the routing table is updated.