Why EIGRP Is Considered As the Best Routing Protocol

Transcription

1 Why EIGRP Is Considered As the Best Routing Protocol Anurag Misra Training Specialist Higher Institute of Plastic Fabrication Riyadh, Saudi Arabia ABSTRACT This paper concentrates upon one of the most popular routing protocol, which is Enhanced Interior Gateway Routing Protocol (EIGRP). In this paper we will provide a detailed introduction of EIGRP and its functions as well as features. We will see how EIGRP works to provide best routes and how it converges at the time of selected route failure. After collecting all the details about EIGRP, we will make a comparison of EIGRP with some other routing protocols and will try to establish a firm foundation to show why and how EIGRP is best routing protocol. General Terms Distance, Vector, Packet Delivery, Delay, Route Update, Routing, Transmission Units. Keywords EIGRP, RIP, Successor, Metrics, Frame Relay, IP Address, Topology, Feasible Successor, Path Discovery 1. INTRODUCTION When we talk about computer networks, first and most important thing which comes to our mind is routing. Biggest challenges in data transfer are, how to find loop free shortest path from source to destination, how to handle route failure and how to reduce convergence time at the time of failure. To address all of these problems, we have various routing protocols. Each and every routing protocol tries to provide answers to above mentioned problems in its own way. Some of the available routing protocols are EIGRP, IGRP, OSPF and RIP etc. For this paper we study about EIGRP in detail. Although some of the features and function of other protocols will also be covered but that will be very limited. Its only will be used to make comparison with EIGRP. So, we can see that where EIGRP stands performance wise. 2. Enhanced Interior Gateway Routing Protocol (EIGRP) Enhanced Interior Gateway Routing Protocol is an advanced distance vector routing protocol. Although basically EIGRP is a Distance Vector Protocol but some properties shown in EIGRP are quite like Link State protocols. The main reason for the development of EIGRP is to provide support for classless IPv4 addresses which was not available in its predecessor IGRP and to have a protocol which can be used with any type of media or network topology. EIGRP is designed to use network resources efficiently and can provide very fast convergence. EIGRP is developed using Diffusing Update Algorithm (DUAL). EIGRP is completely depends upon neighbour relationship. A router in EIGRP trusts its neighbours completely for any information on topology changes or failures. In EIGRP two devices are called neighbours if both of them can exchange hello packets. To establish neighbour relationship and to maintain its tables EIGRP uses five types of packets: Hello Packets Acknowledgement Packets, Query Packets > RJSITM: Volume: 06, Number: 05, March 2017 Page 17

2 Update Packets and Reply Packets EIGRP not only have 5 types of messages but it also maintains three different tables to support routing. Neighbour Table Topology Table and Routing Table To understand these tables structure and how these tables are maintained we have to look in to Figure 1 which has three routers 0, 1 and 2. We will make tables in reference with router / 24 Figure 1 First table is neighbour table. In EIGRP every router keeps record of its neighbour in neighbour tables. This table contains neighbour routers and the interface to which those neighbours are connected. In figure 1, Router 1 has two neighbour routers. So, neighbour table of router 1 will have 2 entries which are shown in table 1. Table 1 Neighbour table of Router 1 Neighbour Interface Router 0 S0 / 0 / 0 Router 2 S0 / 0 / 1 The command used to view the content of EIGRP neighbour table of router is show ip eigrp neighbor Next table is Topology Table. In this table router stores all available routes for destined network. Topology table has four entries for each path. Network Address of destined network. Neighbour Neighbour router through which that network can be reached. Advertised distance this is the distance from neighbouring router to the destination network. Feasible distance this is the distance from current router to destined network. For example in figure 1, if we send data from router 1 to network / 24. Router 1 has two possible paths to send the data, one via router 0 and another via router 2. So Topology table entries will be like Table 2: Table 2 Topology table of Router 1 to reach network / 24 Network Neighbour Advertised distance Feasible distance / 24 Router / 24 Router > RJSITM: Volume: 06, Number: 05, March 2017 Page 18

3 The command used to view the content of EIGRP topology table of router is show ip eigrp topology Best route will be the one which has lowest feasible distance. In our example that will be route via Router 0 because it has the lowest feasible distance 2500 better than 3000 of Router 2. This path will be called Successor and this will go to the third and very last table maintained by EIGRP which is called Routing table. Routing table has the same structure as the topology table but unlike topology table it doesn t store all possible paths for a route but only the best one. Table 3 Routing table of Router 1 to reach network / 24 Network Neighbour Advertised distance Feasible distance / 24 Router The command used to view the content of EIGRP routing table of router is show ip route Only successor is stored in routing table but rest of the paths also not discarded. Instead of discarding all remaining paths EIGRP first checks if other paths can be stored as feasible successor to be used at the time of failure. A criterion to select a path as a feasible successor is that the advertised distance of feasible successor has to be less than the feasible distance of successor. In our example path through Router 2 has the cost of 2000 for its advertised distance which is less than feasible distance of 2500 for the path through Router 0. So, the path through Router 2 can be a feasible successor. Metric shown in advertised distance and feasible distance is calculated by a composite formula which includes almost all the parameters which can affect the data transmission like Bandwidth, Delay, Load and reliability. Apart from these parameters in this formula we also have 5 constant values, which are called K 1, K 2, K 3, K 4 and K 5. The formula to calculate metrics is: K! Bandwidth! + K! Bandwidth! + K 256 Load! Dealy! Metrics = Formula 1 Composite Metrics formula with all 5 parameters K! K! + Reliability 256 Formula has 5 K values and each of them is related with a parameter. Out of this five EIGRP uses 4 components to calculate metrics. Still to understand this formula clearly, we have to look into some details about its components and the K values related to them. We will show this in Table 4. > RJSITM: Volume: 06, Number: 05, March 2017 Page 19

4 Table 4 Components of Metric Formula of EIGRP and Related K Values Component Description K Value Default Value Bandwidth E This is the minimum scaled bandwidth of the route using following formula: Scaled Bandwidth = (10 7 / minimum K 1 1 bandwidth in kbps) It s always >= 0. Load Worst effective load on route, values lies between and based on packet rate K 2 0 Delay E Cumulative interface delay, in tens of microseconds. K 3 1 Scaled Delay = Delay / 10 Reliability Successful packet transmission shown in number between means No Reliability K means 100% Reliability MTU Size of minimum maximum transmission unit of the route. It s always >= 0. K 5 0 Mostly MTU doesn t actively take part in metrics Calculation, so value of defined as 1.!!!!!!"#$%&$#$'( is If values of all the K values are set to their defaults the composite formula becomes: Metrics = Bandwidth! + Dealy! 256 Formula 2 Composite metrics formula with only Bandwidth and Delay as parameter It is very clear by the formula that EIGRP considers almost all the parameters important for routing. This ensures reliability of the selected route. Values of all K values can be configured to produce different routing behaviours. But most of configurations by default use only bandwidth and delay metrics, in that too bandwidth takes precedence. 3. Comparative Study As we have seen EIGRP metrics calculation is quite different than other routing protocols. EIGRP s protocol type is also somewhat different than other protocols. This affects the performance of EIGRP to a great extent but when you talk about routing protocols there are lots of things needed to be considered. So, we would like to take some of the parameters to compare EIGRP with OSPF, IS-IS and RIP and instead of going in detailed version, we represent this comparison in tabular form. Table 4 is there to show the comparison of EIGRP with above mentioned protocols for more than 20 different parameters. This will be easy to understand and evaluate when we have everything arranged in a table. > RJSITM: Volume: 06, Number: 05, March 2017 Page 20

5 Table 4 Comparative analysis of EIGRP with other routing protocols OSPF, IS-IS AND RIP Protocol Property EIGRP OSPF IS - IS RIP Type Hybrid (Advance Distance Vector) Link State Link State Distance Vector Algorithm DUAL Dijkstra Dijkstra Bellmon - Ford Table Driven / On Demand Hybrid of both Table Driven Table Driven On Demand Convergance Very Fast Fast Fast Slow Need of Hello Message Yes Yes Yes Yes Route Selection Shortest Path First Shortest Path First Shortest Path First Shortest Path First Route Update Triggered Triggered Triggered Periodic 30 Sec Transport Type IP / Port 88 IP / Port 89 Layer 2 UDP / Port 52 Route Update Method / IP Multicast / Multicast / Multicast / Route Mechanism / Maintenance in Routing Table Routing Table Forwarding Information Base Routing Table Updates Sent Only Changes Only Changes Only Changes Full Table Log Neighbor State Administrative Distance Yes Yes Yes Yes Summary - 5, Intenal - 90, External Classless Yes Yes Yes V1-No, V2-Yes Support VLSM Yes Yes Yes V1-No, V2-Yes Hop Count Limit 224 (Default 100) None None 15 Authentication Yes Yes Yes V1-No, V2-Yes Location Supported Metrics Interior or Exterior Interior or Exterior Interior Interior Composite Metric Calculation Cost Cost Hop Count Supported Protocols IP, IPX, DECNet, Appletalk IP IP, CLNS IP Loop Free Yes Yes Yes Yes > RJSITM: Volume: 06, Number: 05, March 2017 Page 21

6 Load Balancing Network Overheads Across 6 equal or unequal cost paths Across 4 equal cost paths Across 6 equal cost paths Less Medium Medium High Across 6 equal cost paths All the features shown in table 4 shows that when it comes to routing protocol EIGRP is better choice. Some highlights for EIGRP features are that it provides more protocols support, load balancing for unequal cost paths and convergence in EIGRP is way faster than others. Still if have some practical data for convergence that will make it far more concrete than just mentioning the fact that convergence in EIGRP is not only faster but lot more secure than other protocols. 4. Comparison for Packet Loss at the time of failure for EIGRP, OSPF and RIP In this scenario five routers and two end station are used to collect the data. Both the end stations are connected with router 1 and router 3 respectively. Two paths are available to reach from router 1 to router 3. Path 1 is through router 2 and Path 2 is though router 4 and router 5. Obviously the best route or the successor will be the path 1. Table 5 shows the convergence and re-convergence time for all three protocols. Table 5 Convergence time in seconds for EIGRP, OSPF and RIP Protocol Initial Convergence Re-convergence EIGRP OSPF RIP Now if we look for packet loss following charts will make it more clear that which protocol is more secure than others. To collect the data a packet generator software is used to generate packets at the rate of 5 packets/sec, 10 packets/sec, 15 packets/sec, 20 packets/sec and 25 packets/sec. All these packets are collected with packet capture software. After analysing these captured packets, the packet loss is calculated. Each of three charts represents the packet loss data for one of the selected protocol. > RJSITM: Volume: 06, Number: 05, March 2017 Page 22

7 5. Conclusion Comparative data in Table 5 shows it that for the initial convergence EIGRP is a bit better that OSPF and RIP. RIP comes as worst in all three of them. But when we talk about re-convergence still RIP is worst one but EIGRP is a clear winner in re-convergence, managing to re-route the traffic within few milliseconds. Even for the packet loss EIGRP comes as the best routing protocol in all three selected protocols. While packet loss goes till more than 300 packets in RIP even more than 100 in OSPF, in EIGRP its still in fifties. This clearly makes EIGRP the best choice among its competitors and to add more EIGRP is the only protocol which can scale in a Dynamic Multipoint Virtual Private Network (DMVPN). > RJSITM: Volume: 06, Number: 05, March 2017 Page 23

8 6. REFERENCES [1] Routing Protocol Convergence Comparison using Simulation and Real Equipment, D. Sankar and D. Lancaster, Advances in Communications, Computing, Networks and Security 10. [2] Performance Comparison of Mixed Protocols Based on EIGRP, IS-IS and OSPF for Real-time Applications, S. Farhangi, A. Rostami and S. Golmohammadi, Middle-East Journal of Scientific Research 12 (11): , 2012 ISSN [3] "AN EMPIRICAL COMPARATIVE ANALYSIS ON ASSORTED ROUTING PROTOCOLS", Er. Simranjeet Sandhu and Deepinder Singh Wadhwa, International Journal or Electrical, Electronics and Mechanical Controls, Volume 2 Issue 1 January [4] "Comparison of RIP, EIGRP, OSPF, IGRP Routing Protocols in Wireless Local Area Network (WLAN) by using OPNET Simulator tool - A Practical Approach", P. Kalamani, M. Venkatesh Kumar, M. Chithambarathanu, Reji Thomas, IOSR Journal of Computer Engineering (IOSR-JCE) ISSN: , Volume 16, Issue 4, Ver. VI, Jul Aug. 2014, Page [5] Classification of Routing Protocol in Mobile Ad Hoc Networks: A Review, Vishal Pahal,* Amit Verma, Payal Gupta, IJCSET, November 2011, Vol 1, Issue 10, [6] AN EMPIRICAL COMPARATIVE ANALYSIS ON ASSORTED ROUTING PROTOCOLS, Er. Simranjeet Sandhu, Deepinder Singh Wadhwa, International Journal of Electrical, Electronics and Mechanical Controls, Volume 2 Issue 1 January 2013 [7] Comparison of RIP, EIGRP, OSPF, IGRP Routing Protocols in Wireless Local Area Network (WLAN) by using OPNET Simulator tool - A Practical Approach, P. Kalamani1, M. Venkatesh Kumar2, M. Chithambarathanu3, Reji Thomas, IOSR Journal of Computer Engineering (IOSR- JCE) e-issn: ,p-ISSN: , Volume 16, Issue 4, Ver. VI (Jul Aug. 2014), PP [8] On the Performance comparison of RIP, OSPF, IS-IS and EIGRP routing protocols, Vasos Hadjioannou " [9] Performance Analysis of RIP, EIGRP, and OSPF using OPNET Don Xu and Ljiljana Trajković " [10] EIGRP Metric K values Explained with Example, Computer Networking Basic Tutorials and Study Guides, > RJSITM: Volume: 06, Number: 05, March 2017 Page 24