The Pros and Cons of OSPF and EIGRP

Open Shortest Path First (OSPF) is an interior gateway routing protocol developed for IP networks based on the shortest path first or link-state algorithm originated by Edgars Djikstra. Djikstra states that OSPF’s metric is cost on Cisco routers; cost is based on bandwidth the default value is 10 to the 8^th power divided by interface bandwidth. OSPF adds the cost of each link along the path to the destination network. The SPF algorithm uses this metric to build a tree containing the shortest or “least cost” path to each network.

OSPF was mentioned having many new features, but noted are:

Scalability – OSPF is specifically designed to operate with larger networks.

Full subnetting support – OSPF can fully support subnetting

Hello packets – OSPF uses small hello packets to verify link operation with out transferring large tables

TOS routing – OSPF can route packets by different criterion based on their type of service field

Tagged routes – Routes can be tagged with arbitrary values, easing interoperation.

The main advantage of link state routing (OSPF) is that complete knowledge of topology allows routers to calculate routes that satisfy the incoming request. Which can be useful for traffic engineering purposes where routes can be manipulated to meet different service requirements.

The main disadvantage of a link state protocol is that it does not scale well as more routers are added to the routing domain. By adding more routers increases the size and frequency of the topology updates, and also the length of time it takes to calculate end-to-end routes. This creates a very large OSPF database, using a large amount of memory, which would adversely affect the network integrity. This lack of scalability means that a link state routing protocol is unsuitable for routing across the Internet at large, and is also reason why Imps only route traffic within a single AS.

Enhanced Interior Gateway Protocol (EIGRP), a Cisco proprietary routing protocol, evolved from the evolution of its predecessor IGRP. EIGRP was developed to be used with any media and network topology. It uses an algorithm called DUAL (Diffuning Update Algorithm) to calculate a loop free path to each network. Which has proven most idea for multi levels of hierarchy because of the ability to summarize at any router interface.

Since you can summarize at any interface: it reduces the amount of update traffic, it reduces the length of routing tables, and sets boundaries for queries.

Bounding queries is an important consideration. When a router loses its path to a network and doesn’t have backup. Then it must query all its neighbors. If those routers don’t have the backup path either, then they must query their neighbors and so on. No router can answer its neighbor’s query until all queries have been answered. EIGRP also adapts itself to various types of network links. It sends hello messages less frequent on slow links.

EIGRP key capabilities that distinguish it from other routing protocols include:

Fast convergence – a router stores all its neighbors routing tables so that it can quickly adapt to alternate routes.

Variable length subnet mask – it supports variable length subnet masks permits routes to be automatically summarized on a network.

Support for partial updates – EIGRP sends partial updates when the metric for a route changes. Propagation of partial updates is automatically bounded so that only those routers that need the information are updated.

Support for multiple network layer protocols – EIGRP supports AppleTalk which redistributes routes learned from RTMP, IP redistributes routes learned from OSPF and RIP, ISIS, EGP, and BGP, and Novell NetWare implementation redistributes routes learned from Novell RIP or SAP.

In conclusion, Open standard link state protocol (OSPF) main advantage of link state routing is that complete knowledge of topology allows routers to calculate routes that satisfy the incoming request. On the down side of a link state protocol is that it does not scale well as more routers are added to the routing domain. As for Enhanced Interior Gateway Routing Protocol (EIGRP) advantages are It use of DUAL (Diffuning Update Algorithm) which calculates a loop free path to each network. Which has proven most idea for multi levels of hierarchy because of the ability to summarize at any router interface. EIGRPs disadvantages are by default automatically summarize routes at the classful boundaries. Similar to that of RIP and IGRP. After carefully analyzing both the pros and cons of both OSPF and EIGRP I believe EIGRP has more versatility and adaptability than its OSPF rival.