Comparing RIPv1 & RIPv2
This page will provide some more information about how RIP works. It will also describe the differences between RIP v1 and RIP v2. RIP uses distance vector algorithms to determine the direction and distance to any link in the internetwork. If there are multiple paths to a destination, RIP selects the path with the least number of hops. However, because hop count is the only routing metric used by RIP, it does not necessarily select the fastest path to a destination.
RIP v1 allows routers to update their routing tables at programmable intervals. The default interval is 30 seconds. The continual sending of routing updates by RIP v1 means that network traffic builds up quickly.
To prevent a packet from looping infinitely, RIP allows a maximum hop count of 15. If the destination network is more than 15 routers away, the network is considered unreachable and the packet is dropped. This situation creates a scalability issue when routing in large heterogeneous networks. RIP v1 uses split horizon to prevent loops. This means that RIP v1 advertises routes out an interface only if the routes were not learned from updates entering that interface. It uses holddown timers to prevent routing loops. Holddowns ignore any new information about a subnet indicating a poorer metric for a time equal to the holddown timer.
RIP v2 is an improved version of RIP v1. It has many of the same features of RIP v1. RIP v2 is also a distance vector protocol that uses hop count, holddown timers, and split horizon.
The TTL field in the IP packet forces the packet to be dropped When the hop count reaches 15 routers. The network is considered unreachable, and the packet is dropped because the router doesn't have a route to the destination network.