Chapter 4 Router Communication Protocol

4.1 RIP- Router Information Protocol

The routing information Protocol (RIP) is a distance-vector protocol that used to exchange routing information between routers. RIP uses broadcast User Datagram Protocol (UDP) data packets to exchange routing information and rip is based on distance-vector algorithm. This routing protocol is determines the best path through an Internet by looking at the number of hops between the two end nodes. The maximum hops count for RIP is 15 hops.

4.1.1 Routing loops

There is problem with distance-vector routing protocol, which is router cannot acquaint with the whole status of network. Routers have to get network reachable information depending on neighboring routers and RIP also comes up against slow convergence, which will introduce inconsistence. The following methods that used by RIP to decrease possibility of routing loop: spilt horizon, spilt horizon with poison reverse, Holddown timer and triggered update.

4.1.1.1 Spilt Horizon

The spilt horizon is a technique for preventing reverse routes between two routers. The rule of spilt horizon is that router never advertised the cost of a destination to neighbor if it is the current next-hop for the destination.

4.1.1.2 Spilt Horizon with Poison Reverse

The rule for “split horizon” is when sending updates out a particular interface, designate any networks that were learned from updates received on that interface as unreachable. This mean is when an interface is up; the router records from which interface a route comes, and not sends the route back to this interface.

4.1.1.3 Holddown timer

Holddown timer is able to prevent a router from receiving new routing information that was just removed from routing table. The default holddown timer is 180 seconds.

4.1.1.4 Triggered update

Split horizon with poisoned reverse will break any loop of two routers. However, it is still possible for loops of three or more routers, to occur. This loop will break only when infinity (presented as 16) will be reached. Triggered updates are an attempt to speed up this

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