3-2z Metric: Cost from the local router to the destination.z Route time: Time elapsed since the routing entry was last updated. The time is reset to 0 every timethe routing entry is updated.RIP timersAs defined in RFC 1058, RIP is controlled by three timers: Period update, Timeout, andGarbage-collection.z Period update timer: The period update timer defines the interval between routing updates.z Timeout timer: The timeout timer defines the route aging time. If no update for a route is receivedafter the aging time elapses, the metric of the route is set to 16 in the routing table.z Garbage-collection timer: The garbage-collect timer defines the interval from when the metric of aroute becomes 16 to when it is deleted from the routing table. During the Garbage-Collect timerlength, RIP advertises the route with the routing metric set to 16. If no update is announced for thatroute after the Garbage-Collect timer expires, the route will be deleted from the routing table.Routing loops preventionRIP is a distance-vector (D-V) based routing protocol. Since a RIP router advertises its own routingtable to neighbors, routing loops may occur.RIP uses the following mechanisms to prevent routing loops.z Counting to infinity. The metric value of 16 is defined as unreachable. When a routing loop occurs,the metric value of the route will increment to 16.z Split horizon. A router does not send the routing information learned from a neighbor back to theneighbor to prevent routing loops and save the bandwidth.RIP Startup and OperationThe whole process of RIP startup and operation is as follows:z Once RIP is enabled on a router, the router broadcasts or multicasts a request packet to itsneighbors. Upon receiving the packet, each neighbor running RIP answers a response packetcontaining its routing table information.z When this router receives a response packet, it updates its local routing table and sends atriggered update packet to the neighbors. Upon receiving the triggered update packet, the neighborsends the packet to all its neighbors. After a series of update triggering processes, each router canget and keep the updated routing information.z By default, RIP sends its routing table to its neighbors every 30 seconds. Upon receiving thepackets, the neighbors maintain their own routing tables and select optimal routes, and thenadvertise update information to their respective neighbors so as to make the updated routes knownglobally. Furthermore, RIP uses the aging mechanism to handle the timeout routes to ensurereal-time and valid routes.RIP Configuration Task ListComplete the following tasks to configure RIP:Task RemarksConfiguring Basic RIPFunctionsEnabling RIP on the interfaces attached to a specified networksegment Required
