The automatic and dynamic exchange of routing information between routers is made possible by routing Protocols. As different networks are implemented in different ways, many routing protocols are available, each with its own set of advantages and disadvantages. Enhanced Interior Gateway Routing Protocol (EIGRP) and Open Shortest Path First (OSPF) are two of the most widely deployed routing protocols currently. EIGRP vs. OSPF will give a better understanding of both routing protocols.

In this blog, we are going to talk about the differences between OSPF and EIGRP. We will be comparing both protocols based on the category they both fall into, how they are different on the basis of their metrics, their Administrative Distance, their timers, and load balancing. So let's get started and understand the differences between these two AMAZING routing protocols.

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Let's first try to understand the different categories of routing protocols. We can broadly categorize the routing protocols into three types:

• Distance Vector
• Link State
• Path Vector

1. Distance Vector: The distance vector protocol tells us in which direction one should be moving to reach the destination and how far the destination is. The protocol doesn’t care about the entire path we have to go; it guides us about the next hop’s direction and the cost, representing how far the destination is in that particular direction. RIP (Routing Information Protocol) falls under this category. EIGRP is also a part of this category. Still, it’s an advanced distance vector protocol due to its usage of the DUAL (Diffusing Update Algorithm) algorithm which improves the efficiency of the protocol.
2. Link State: Link state protocols work with the Dijkstra algorithm. Let's understand this through the example of Google/Apple maps. These navigation applications show you the best path and have the complete map in the system; the same is the case with the Link State protocols. These protocols have the map of the entire topology that you will be traversing, and according to the cost calculations, the protocol will provide you the best path with the sequence of next hops that would help you reach the destination quickest. All the routers within the same area of the topology will have a complete understanding of the entire topology. OSPF falls under this category.
3. Path Vector: This category includes the famous BGP (Border Gateway Protocol) internet protocol. Path Vector protocols provide information about the direction and path in terms of Autonomous Systems you have to traverse to reach a destination.

Now, let's move on to discuss the major topic, i.e., EIGRP vs OSPF.

Difference between OSPF and EIGRP

In OSPF, different routers understand different parts of topology, which they share with each other using LSAs (Link State Advertisements). Using these LSAs, they collect information on the whole topology. On the other hand, EIGRP uses the Reliable Transport Protocol (RTP) to send, control, and acknowledge EIGRP updates under DUAL to find the best loop-free route.

Let's see the difference between OSPF and EIGRP on the basis of various metrics.

EIGRP vs OSPF - On the basis of Administrative Distance

Administrative Distance is simply the value that defines the trustworthiness of any route. The lesser the AD better the route. For example, if a router learns about the network 192.168.1.0 from 3 different routers, the decision to find the best out of them would depend upon the source of information. Now let's assume that 1st route was learned via Static Routing, 2nd via RIP, and 3rd via EIGRP.

In this scenario, the 1st route will be installed into the routing table considering the lowest AD associated with the source. In any scenario, the most believable route would be a directly connected route, as it has an AD of 0. Next, preference is given to the static route with the AD of 1.

Now let's talk about the protocols we are comparing in this blog. EIGRP routes have an AD of 90, whereas OSPF has an AD of 110 which means EIGRP would be given preference in case a route is learned via both protocols. These values are correct when the routes are learned within the same autonomous system. If the routes are getting redistributed from a different autonomous system, the AD of EIGRP routes will be 170, and in the case of OSPF, it remains the same, i.e., 120.

EIGRP vs OSPF - On the basis of Metric, they use

OSPF uses the metric of cost, and the path having the lowest cost is elected as the best path to reach the destination. OSPF costs can be calculated by dividing the reference bandwidth (default is 100 Mbps) by the link bandwidth. In EIGRP, the path selection depends on factors like Bandwidth, Delay, Load, MTU, and Reliability. Because load and reliability are dynamic variables, EIGRP's default metric calculation values are Bandwidth and Delay.

To learn about the metrics of these two protocols in detail, you can click here - EIGRP and OSPF Metric Calculation.

OSPF Cost Calculation -

EIGRP Cost Calculation -

EIGRP vs OSPF - On the basis of Timers

Both the routing protocols, to discover and know about their neighbours, send out hello messages periodically after some interval of time. This interval, known as the hello timer in the case of EIGRP is 5 seconds and 10 seconds in the case of OSPF. And then, there has to be some timer that defines how long a router should wait in case it is not receiving a hello message from the neighbour. This is the case of EIGRP, known as hold-timer, and 3 times of hello time (15 seconds); in the case of OSPF, it is known as dead-interval and is of 4 times of hello time (40 seconds).

Other than the values, another difference between the Hold Time and Dead interval is that Dead Interval defines how long a router will wait for the neighbour to send the hello message. In contrast, hold time is the information we will send to our neighbour telling them to wait for this long in case you stop receiving hello messages from me.

EIGRP vs OSPF - On the basis of Load Balancing

Both protocols by default support equal cost load balancing, meaning if we have more than 1 best route to reach any specific destination, then the data will be distributed on all of the links. In EIGRP, we also see the support for unequal cost load balancing, which can be achieved by manipulating the variance, which is the multiplier of path cost. The good part is that EIGRP intelligently sends proportionally higher traffic on the better links among the available links.

These are the differences between OSPF and EIGRP. Given you are still with us, you must have a good understanding of both these protocols.

Conclusion

EIGRP and OSPF are the most widely utilized IGPs today. Both are widely used in corporate networks and are quite mature and robust in their deployment and operation. The goal of this blog is to compare EIGRP vs OSPF to offer you an overview of each protocol and an understanding of the difference between OSPF and EIGRP. In the end, the kind of protocol that works best for your particular network will be determined by several different factors.