Differences between distance vector (RIP) and link-state (OSPF) routing protocols: The following are advantages of link-state routing protocols (OSPF): * Link-state protocols use cost metrics to choose paths through the network. The cost metric reflects the capacity of the links on those paths. * An LSA exchange is triggered by an event in the network instead of periodic updates. This speeds up the convergence process because there is no need to wait for a series of timers to expire before the routers can converge. * Each router has a complete and synchronized picture of the network.
Therefore, it is very difficult for routing loops to occur. * Routers use the latest information to make the best routing decisions. * The link-state database sizes can be minimized with careful network design. This leads to smaller Dijkstra calculations and faster convergence. * Every router, at the very least, maps the topology of its own area of the network. This attribute helps to troubleshoot problems that can occur. The following are some disadvantages of link-state routing protocols: * They require more memory and processor power than distance vector protocols. This makes it expensive to use for organizations with small budgets. They require strict hierarchical network design, so that a network can be broken into smaller areas to reduce the size of the topology tables. * They require an administrator who understands the protocols well. * They flood the network with LSAs during the initial discovery process. This process can significantly decrease the capability of the network to transport data. It can also noticeably degrade the network performance. An overall comparison between both routing protocols used in this lab follows: 1. RIP is appropriate for small networks, and the best path is based on the lowest number of hops.
OSPF is appropriate for large, scalable internetworks, and the best path is determined by the speed of the link. 2. RIP and other distance vector protocols use simple algorithms to compute best paths. The SPF algorithm is complex. Routers that implement distance vector protocols need less memory and less powerful processors than those that implement OSPF. 3. OSPF guarantees loop-free routing. Distance vector protocols may cause routing loops. 4. In large networks RIP convergence can take several minutes since the routing table of each router is copied and shared with directly connected routers.
After initial OSPF convergence, maintaining a converged state is faster because only the changes in the network are flooded to other routers in an area. 5. RIP selects a path to a network by adding one to the hop count reported by a neighbour. It compares the hop counts to a destination and selects the path with the smallest distance or hops. This algorithm is simple and does not require a powerful router or a lot of memory. RIP does not take into account the available bandwidth in best path determination. 6. OSPF selects a path using cost, a metric based on bandwidth.
All OSPF routers must obtain complete information about the networks of every router to calculate the shortest path. This is a complex algorithm. Therefore, OSPF requires more powerful routers and more memory than RIP. 7. RIP uses a flat topology. Routers in a RIP region exchange information with all routers. OSPF uses the concept of areas. A network can be subdivided into groups of routers. In this way OSPF can limit traffic to these areas. Changes in one area do not affect performance in other areas. This hierarchical approach allows a network to scale efficiently.