Performance Comparison of Two Dynamic Routing Protocols: RIP and OSPFABSTRACT: There are two main classes of adaptive routing protocols in the internet: distance vector and link state. This paper presents the comparison between distance vector and link state. It also outlines the pros and cons of RIP and OSPF protocols and a performance analysis with some possible enhancement is presented. Network Simulator (NS2) is used to obtain the performance results of the two classes using different metrics such as throughput, packet delay and packet loss. Results of the simulation show that OSPF has a better performance than RIP in terms of average throughput and packet delay in different network sizes, while RIP is better than OSPF in terms of number of packet loss in large networks.Keywords: Dynamic Routing Protocols, RIP, OSPF, NS21.INTRODUCTION Networks rely on routing protocols to keep the routing tables updated. Routing is used in networks to control and forward data. For a router to be efficient and effective, the critical factor is the choice of the routing protocol. Routing protocols find a path between network nodes; if multiple paths exist for a given node then the shortest path is selected by protocol. Each protocol has a cost metric that it applies to each path. The path with lowest metric is selected by protocol. Metrics to compare one routing protocol with another are based on convergence time to adapt to topology changes, optimality is to choose the best path, not necessarily at minimum cost but to ensure a minimum delay or to minimize overhead and space requirements to store the routing table 157. The rest of paper is organized as follows: Section 2 is an overview of routing protocols. In Section 3 and 4 RIP and OSPF are discussed. We studied RIP and OSPF because this interior routing protocol is widely used in the internet. In addition the pros and cons of these routing protocols are studied in brief. In Section 5 the system model used for simulation is examined, and in Section 6 we implement routing protocols using NS2. The results of simulation show that OSPF is better than RIP in some aspects. But in other aspects RIP is revealed to be better than OSPF in Section 7. Finally we conclude the paper. 2.ROUTING PROTOCOLS There are two types of routing protocols: static or dynamic routing protocols. Dynamic routing protocols are superior over static routing protocols because of its scalability and adaptability features.Dynamic routes are learned by communicating each router with another, when a new router is added or an old router is removed, the router learns about changes, updates its routing tables, and informs the other router about the modification. The classification of a routing protocol is either as an interior or exterior gateway protocol. The interior gateway protocol runs an algorithm within an Autonomous System (AS) and the exterior gateway protocol runs an algorithm outside an AS. The interior gateway protocol is classified into two groups: either distance vector (DV) or link state (LS). The distance vector selects the best routing path based on a distance metric, while link state selects the best routing path by calculating the state of each link in a path and finding the path that has the lowest total metric to reach the destination 15. The parameters used in order to evaluate the algorithm / s performance are: 713 . Instantaneous Packet Delay: This is the average delay of all data packets routed successfully from source to destination for a given period during an algorithm simulation. Instantaneous Throughput: This is the number of packets successfully routed for a given time during an algorithm simulation. Packet Loss: This refers to the number of packets that are lost. Different features of LS and DV protocols are presented in 146. In 14 they enhance the RIP to provide stability and reduce overhead of message updates. In 12 and 13 they enhance OSPF by using QoS. In 5 it is shown that OSPF is better than RIP in throughput, packet delay, packet loss and other aspects. 3.ROUTING INFORMATION PROTOCOL (RIP) RIP is an interior routing protocol that is based on DV routing. RIP uses hop count to calculate the best route. It is simple but has many drawbacks. RIP uses hop count as a cost metric for each link, and each link has a cost of 1. The maximum path cost is 15 so RIP is limited to use in ASs that are not larger than 15 hops. Every 30 seconds the router sends copy of the routing table to its neighbors. The routing table is updated whenever the network topology is changed; each router informs its adjacent neighbors about the updating in the routing table. When the router receives an update, first it compares the new route with the current routing table, then adds a new path to the routing table and informs its adjacent neighbors about the updating in the routing table 5