RIP

DIFFRENCE RIP & EIGRP

ENSC 427: COMMUNICATION NETWORKS SPRING 2014 FINAL PROJECT Comparison of RIP, OSPF and EIGRP Routing Protocols based on OPNET Project Group # 9 http://www.sfu.ca/~sihengw/ENSC427_Group9/ Justin Deng Siheng Wu Kenny Sun 301138281 301153928 301154475 zda9@sfu.ca sihengw@sfu.ca yujuns@sfu.ca Table of Contents List of Figures………………………………………………………………………….……..….1 Abstract..........................................................................................................................................2 1. Introduction................................................................................................................................3 1.1 Routing Protocol Basics ……….……………………………………...….…………………..3 1.2 Routing Metrics Basics ……………...…..…………………….………………………….….3 1.3 Static Routing and Dynamic Routing ………………………………………………………..3 1.4 Distance Vector and Link State ……………………………………………………………...3 2. Three Routing Protocols………………………………………………….………………..….4 2.1 Routing Information Protocol (RIP) ……….…………………………….…………………...4 2.2 Open Shortest Path First (OSPF)………..…………………….…………………………...….5 2.3 Enhanced Interior Gateway Routing Protocol (EIGRP) …….....……………………………..7 3. OPNET Simulations………………………………………………………………………......8 3.1 Topologies ……………………………….…………………………………………………...8 3.1.1 Mesh Topology ………..………….……………………………………………………....8 3.1.2 Tree Topology ……………………..……………………………………………………...9 3.2 Simulation Setup …………………………………………………………………………….10 3.2.1 Simulation Setup for Failure/Recovery Configuration...........…………………………...10 3.2.2 Simulation Setup for Individual DES statics…....………….……………………………10 3.2.3 Simulation Setup for Simulation Global Attributes.……………………………………..11 3.2.4 Model Attributes ………………………………………………………………………...12 4. Result and Analysis ……………………………………………………………………….....14 5. Conclusion…………………..…………………………………………………………….….20 5.1 Future work and difficulties ....................................................................................................21 References…………………………………………………………………………………….…22 1 List of Figures Figure.1 Simple structure of OSPF……………………………………………………………….5 Figure.2 Shortest path tree................................…………………………………………………...6 Figure.3 Area......................................................………………………………………………….6 Figure.4 Basic structure of Mesh topology..........………………………………………………....9 Figure.5 Basic structure of Tree topology.....……………………………………………………..9 Figure.6 Failure/Recovery Configuration.......…………………………………………………...10 Figure.7 RIP DES statics ………………………………………………………………………..10 Figure.8 OSPF DES statics...............................………………………………………………….11 Figure.9 EIGRP DES statics…............…………………………………………………………..11 Figure.10 Simulation Global Attributes..………………………………………………………...12 Figure.11 Simulation Global Attributes.....………………………………………………………12 Figure.12 RIP parameters............………………………………………………………………..12 Figure.13 OSPF parameters ....…………………………………………………………………..13 Figure.14 EIGRP parameters ……...…………………………………………………………….14 Figure.15 Overlaid Convergence Activity on small mesh....…………………………………….15 Figure.16 Overlaid Convergence Activity on mesh……………………………………………..15 Figure.17 Overlaid Convergence Activity on tree...……………………………………………..16 Figure.18 Overlaid Convergence Activity on tree...……………………………………………..17 Figure.19 OSPF Average Convergence Duration over different topologies.......………………..17 Figure.20 EIGRP Average Convergence Duration over different topologies...…………………18 Figure.21 Traffic sent comparison on small mesh topology....…………………………………..18 Figure.22 Traffic sent comparison on mesh topology....…….........……………………………..19 Figure.23 Traffic sent comparison on tree topology ……........................................…………….20 2 Abstract In a computer network, the transmission of data is based on the routing protocol which selects the best routes between any two nodes. Different types of routing protocols are applied to specific network environment. Three typical types of routing protocol are chosen as the simulation samples: RIP, OSPF and EIGRP. RIP (Routing Information Protocol) is one of the oldest routing protocols still in service. Hop count is the metric that RIP uses and the hop limit limits the network size that RIP can support. OSPF (Open Shortest Path First) is the most widely used IGP (Interior Gateway Protocol) large enterprise networks. OSPF is based on the Shortest Path First (SPF) algorithm which is used to calculate the shortest path to each node. EIGRP Enhanced Interior Gateway Routing Protocol) is Cisco's proprietary routing protocol based on Diffusing Update Algorithm. EIGRP has the fastest router convergence among the three protocols we are testing. More detailed description of these three routing protocols will be included later. We aim to analyze the performance of the three protocols such as their router convergence, convergence duration and end-to-end delay. In our project, we are going to use OPNET to simulate RIP, OSPF and EIGRP in order to compare their attributes and performance. According to the convergence we can find out which protocols are suitable for different sizes and types of network. 3 1. Introduction 1.1Routing Protocol Basics A routing protocol is the language a router speaks with other routers in order to share information about the reachability and status of network.(1) It includes a procedure to select the best path based on the reachability information it has and for recording this information in a route table. Regarding to select the best path, a routing metric will be applied and it is computed by a routing algorithm. 1.2Routing Metric Basics A metric is a variable assigned to routers as a means of ranking them from the best to worst or from most preferred to least preferred. (1) Different routing protocols have different metrics. When there is more than one route between two nodes, a router must determine a method of metrics by choose the routing protocol to calculate the best path. 1.3 Static Routing Dynamic Routing Protocols can fall into two groups: static routing and dynamic routing. Static routing is simply the process of manually entering routes into a device‟s routing table via a configuration file that is loaded when the routing device starts up. In static routing, all the changes in the logical network layout need to be manually done by the system administrator. However, dynamic routing allows routers to select the best path when there is a real time logical network layout change. In our project, we will discuss the difference between the EIGRP, RIP and OSPF. All of them are belong to dynamic routing protocols. 1.4 Distance Vector and Link State In addition, most routing protocols can be classified into two classes: distance vector and link state. Distance vector routing protocol is based on Bellman – Ford algorithm and Ford – Fulkerson algorithm to calculate paths. A distance vector routing protocol uses a distance calculation and a vector direction of next hop router as reported by neighboring routers to choose the best path. It requires that a router informs its neighbors of topology changes periodically. Link state routing protocols build a complete topology of the entire network are and then calculating the best path from this topology of all the interconnected networks. It requires more processing power and memory because it has a complete picture of the network. 4 2. Three Routing Protocols 2.1 Routing Information Protocol (RIP) RIP is a standardized vector distance routing protocol and uses a form of distance as hop count metric. It is a distance vector. Through limiting the number of hop counts allowed in paths between sources and destinations, RIP prevents routing loops. Typically, the maximum number of hops allowed for RIP is 15. However, by achieving this routing loop prevention, the size of supporting networks is sacrificed. Since the maximum number of hop counts allowed for RIP is 15, as long as the number goes beyond 15, the route will be considered as unreachable. When first developed, RIP only transmitted full updates every 30 seconds. In the early distributions, traffic was not important because the routing tables were small enough. As networks become larger, massive traffic burst becomes more likely during the 30 seconds period, even if the routers had been initialized at different times. Because of this random initialization, it is commonly understood that the routing updates would spread out in time, but that is not the case in real practice. RIP has four basic timers: Update Timer (default 30 seconds): defines how often the router will send out a routing table update. Invalid Timer (default 180 seconds): indicates how long a route will remain in a routing table before being marked as invalid, if no new updates are heard about this route. The invalid timer will be reset if an update is received for that particular route before the timer expires. A route marked as invalid is not immediately removed from the routing table. Instead, the route is marked with a metric of 16, which means the route is unreachable, and will be placed in a hold-down state. Hold-down Timer (default 180 seconds): specifies how long RIP will keep a route from receiving updates when it is in a hold-down state. In a hold-down state, RIP will not receive any new updates for routes until the hold-down timer expires. A route will go into a hold-down state for the following reasons:  The invalid timer has expired  An update has been received from another router; route goes into a 16 metric (or unreachable).  An update has been received from another router; route goes into a higher metric than what it is currently using. Flush Timer (default 240 seconds): When no new updates are received about this route, flush timer indicates how long a route can remain in a routing table before getting flushed out. The flush timers operates simultaneously with the invalid timer, so every 60 seconds, after it has been marked invalid, the route will get flushed out. When RIP timer is not in sync with all routers on the RIP network, system instability occurs. This timer must be set to a higher value than the invalid timer. 5 2.2 Open Shortest Path First (OSPF) OSPF is defined in RFC 2328 which is an interior Gateway Protocol used to distribute routing information within an AS (Autonomous System). Among all the three chosen samples, OSPF is the most widely used routing protocol in large enterprise networks. OSPF is based on link-state technology by using SPF algorithm which calculates the shortest path. SPF calculation Before running the calculation, it is required that all routers in the network to know about all the other routers in the same network and the links among them. The next step is to calculate the shortest path between each single router. For all the routers they exchange link-states which would be stored in the link-state database. Every time a router receives a link-state update, the information stores into the database and this router propagate the updated information to all the other routers. Below is a simple model of how the SPF algorithm works. Figure 1: Simple structure of OSPF A simple network formed by five routers; all the routers know about all the other routers and links. After all the paths are figured out, the path information are stored in the link database. The link database for the above model is : [A, B, 3], [A, C, 6], [B, A, 3], [B, D, 3], [B, E, 5], [C, A, 6], [C, D, 9], [D, C, 9], [D, B, 3], [D, E, 3] , [E, B, 5] and [E, D, 3]. Each term is referred to the originating router, the router connected to and the cost of the link between the two routers. Once the database of each router is finished, the router determines the Shortest Path Tree to all the destinations. (The shortest path in the SPF algorithm is called the Shortest Path Tree). The Dijkstra Shortest Path First is then running to determine the shortest path from a specific router to all the other routers in the network. Each router is put at the root of the Shortest Path Tree and then the shortest path to each destination is calculated. The accumulated cost to reach the destination would be the shortest path. 6 The cost (metric) of OSPF is the cost of sending packets across a certain interface. The formula to calcite the cost is: cost= 10000 0000 /bandwidth in bps. If the bandwidth is wider, the cost would be lower. Below is a diagram of the structure used to calculate the Shortest Path Tree. Figure 2: Shortest path tree When the Shortest Path Tree is completed, the router will work on the routing table. Areas and Border Routers In OSPF protocol, an Autonomous System can be divided into sections. A section and a nearby router can dorm an AREA. Since each section calculate the Shortest Path using the same algorithm as above, each section has its own database and path tree and the information are invisible outside this section. By doing this, the size of the database can be dramatically reduced. Figure 3: Area 7 In an autonomous, there is a backbone called Area 0 which is the pivot of this autonomous. Area 0 connected to other sections with ABR (Area Border Router) to exchange link-state. Stub Area, Not-So-Stubby Area, Totally Stubby Areas and Totally NSSA are other types of sections with specific functions. Advantages Compare to RIP, OSPF has no limitation due to hops (RIP has a limit of 15 hops so any network with more than 15 hops cannot be achieved by RIP. OSPF can handle Variable Length Subnet Masks (VLSM) but RIP cannot. The most important is that OSPF converges much faster than RIP due to its calculation algorithm. This might not be significant in a small size network but in large enterprise networks, this will be a time out. 2.3 Enhanced Interior Gateway Routing Protocol (EIGRP) The Enhanced Interior Gateway Routing Protocol (EIGRP) is a hybrid routing protocol which provides significant improvements on IGRP. EIGRP replaced IGRP in 1993 since Internet Protocol is designed to support IPv4 addresses that IGRP could not support. Hybrid routing protocol incorporates advantages of both Link-state and Distance-Vector routing protocols, it was based on Distance-Vector protocol but contains more features of Link-State protocol. EIGRP saves all routes rather than the best route to ensure the faster convergence. EIGRP keeps neighboring routing tables and it only exchange information that it neighbor would not contain. EIGRP is commonly used in large networks, and it updates only when a topology changes but not periodically unlike old Distance-Vector protocols such as RIP. Metric is used to determine whether the chosen route is optimized. EIGRP metric is based on its bandwidth, delay, reliability, load and MTU. A default expression for EIGRP metric is 𝑀𝑒𝑡𝑟𝑖𝑐 = 𝐵𝑎𝑛𝑑𝑊𝑖𝑑𝑡ℎ + 𝐷𝑒𝑙𝑎𝑦 ∗ 256. There are four basic components to operate EIGRP, which are