EIGRP vs. OSPF
Enhanced Interior Gateway Routing Protocol (also known as EIGRP) is a proprietary routing protocol developed by Cisco. It is loosely based on the original concept of IGRP –Interior Gateway Routing Protocol. It is an advanced distance vector routing protocol that contains optimisations that are intended to minimise any routing instability that was incurred after topology changes, as well as the bandwidth usage and processing power within the router. Those routers that support EIGRP redistribute route information to IGRP neighbours automatically. These routers accomplish this by converting 32 bit EIGRP metric to 24 bit IGRP metric.
Open Shortest Path First (also known as OSPF) is a dynamic routing protocol. It is used specifically for the Internet Protocol (or IP) networks. It is a link state routing protocol and is most commonly grouped with interior gateway protocols. It operates within a single autonomous system (or AS). OSPF is arguably the most commonly used interior gateway protocol (or IGP) that functions mostly in large enterprise networks.
EIGRP collects data. This data is stored in three tables: the Neighbour Table, which stores data about routers that neighbour the EIGRP (meaning, those that are directly accessible through those interfaces that are directly connected); the Topology Table, which contains the aggregation of the routing tables that are directly gathered from all the neighbours that are directly connected (it contains a list of destination networks in the EIGRP routed network in conjunction with their respective metrics); and the Routing Table, which stores the actual routes to all destinations (it is populated from the data stored on the topology table with every destination network that has its own successor as well as an optional feasible successor that has been identified). EIGRP differs from most other distance vector protocols in that it does not rely on periodic route dumps so it is capable of maintaining its topology table. Information that is to be routed is only exchanged when the new neighbour adjacencies are established –then changes are sent.
OSPF routes IP packets within a single routing domain by gathering link state information from those routers that are available. It then constructs a topology map of the network. This topology determines the routing table that will be presented to the Internet Layer –the Internet Layer makes the decisions about to where information will be routed based only on the destination IP address that’s been found in the IP datagrams. OSPF was designed specifically to support variable length subnet masking (or VLSM) or Classless Inter-Domain Routing (or CIDR) addressing models.
Summary:
1. EIGRP is a proprietary gateway protocol that contains optimisations intended to minimise routing instability incurred after topology changes; OSPF is a dynamic routing protocol that is used specifically for the IP networks.
2. EIGRP collects data in three tables; OSPF routes IP packets within a single routing domain.