Niki Scott
April 22, 2014
NT 2640

Cisco Networks – EIGRP versus OSPF

Categories | EIGRP | OSPF | Type | Advanced Distance Vector | Link – State | Metric | Composite | Cost | Administrative Distance | 120 | 110 | Algorithm | SPF Algorithm fast convergence loop free hop based. Bellman – Ford | Dual algorithm could be in status, query out the whole network shortest path. | Protocol | USP | IP | Topology | Can build a hierarchical and scalable network. | Cannot build a hierarchical network with this protocol. |

The Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance – vector routing protocol that is used on a computer network to help automate routing decisions and configuration. The protocol was designed by Cisco systems as a proprietary protocol, available only on Cisco routers, but Cisco converted it to an open standard in 2013. EIGRP allows a router to share information it knows about the network with neighboring routers within the same logical area known as an autonomous system. Contrary to other well known routing protocols such as routing information protocol, EIGRP only shares information that a neighboring router would not have, rather than sending all of its information. EIGRP is optimized to help reduce the workload of the router and the amount data that needs to be transmitted between routers. The features that support EIGRP are the following; support for Classless Inter-Domain Routing (CIDR) and variable length subnet masking. Routing is not summarized at the classful network boundary unless auto summary is enabled. The support for the load balancing on parallel links between sites is another feature of EIGRP. The ability to use different authentication passwords at different times and MD5 authentication between two routers is some other features of EIGRP. EIGRP sends topology changes, rather than sending the entire routing table when a route is changed. Periodically checks if a route is available and propagates routing changes to neighboring routers if a changes have occurred. The last feature of EIGRP is backwards compatibility with the IGRP protocols.

OSPF-enabled routers use the Shortest Path First (SPF) algorithm to compute the shortest path between nodes on an internetwork. They create a map called the link state database that describes the topology or structure of the router’s specific network area. Network areas are groups of networks connected using OSPF-enabled routers that all have router interfaces for any of the networks included in the area. Areas typically have no more than about 30 or 40 routers and are connected to each other through a designated high-speed contiguous backbone area using area border routers (ABRs). OSPF areas simplify computation of link state information because the computational requirements of calculating link state information rise rapidly as the size and complexity of the network increase. With OSPF areas, each router need maintain only link state information about its own area and other areas connected to it, which improves the scalability of OSPF. The link state information stored in the database (routing table) of each router includes cost information in addition to hop information. Administrators can configure routers in a complex mesh topology network so that specific paths are preferred over others. The SPF algorithm is used so that routing information can be quickly recalculated if routers are moved or if they go down. This feature is known as Fast Convergence. The SPF algorithm also ensures that the routing tables contain the shortest (least-cost) paths and that routing loops do not occur. The link state database of routing information is updated by advertisements using multicasting if a router goes down or if the structure of the network is reconfigured, and the database is used to calculate routes for delivering data over the network. Unlike the older RIP, OSPF uses multicasting to update only routing information, not the entire routing table. And unlike RIP-enabled routers, which broadcast routing information every 30 seconds, OSPF broadcasts changes only when they occur. These features substantially reduce inter-router network traffic compared to RIP and make OSPF a more efficient protocol than RIP for large internetworks.

Cites:
Wikipedia.2014. Enhanced Interior Gateway Routing Protocal. http://en.wikipedia.org/wiki/Enhanced_Interior_Gateway_Routing_Protocol.

The network encyclopedia. 2013. Open Shortest Path First Protocol
http://www.thenetworkencyclopedia.com/entry/open-shortest-path-first-ospf-protocol/