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What Is OSPF (Open Shortest Path First) in Routing?

What Is OSPF (Open Shortest Path First) in Routing?

Understanding OSPF and RIP

As networking design grows more complicated and the scale of your network increases, you need better ways to manage traffic. One tool at your disposal is the routing protocol.

There are many routing protocols in the world, but a handful are dramatically more popular than the rest, and for good reason. One of the leading protocols is OSPF.

In this crash course, you’re going to learn the essentials of OSPF, how it works, where it runs into trouble, and what kinds of applications best suit it.

Understanding OSPF

OSPF is a routing protocol for IP networks. It utilizes link-state routing and interior gateway protocols. These tools enable the construction of topology maps of a network, and those maps are used to optimize pathways for sending and receiving packets.

The entire process is rather complicated and complex, but it boils down to some straightforward ideas. First of those is the network topology. All of the routers in an OSPF network are able to share link-state information with each other. Through this, each router is given a complete topology map that works as a routing table. With these maps and tables, the routers optimize traffic.

It’s worth noting that while OSPF is designed around the concept of shortest path routing, that’s a simplification of some of the powerful ways this protocol can manage traffic. The key algorithm (Dijkastra’s algorithm) does search for the shortest path, but it is capable of searching for weighted paths. In other words, the routers can optimize according to various parameters, allowing for OSPF routing that prioritizes certain types of traffic, minimizing bottlenecks, or catering to any number of other service criteria.

While that covers the very basics of how OSPF works, there are a couple of features and challenges that are equally important.

Designing OSPF

One of the challenges of implementing OSPF in networks is designing the overall system. Routers need to have complete maps of the network in order to function properly with this protocol. That means that an OSPF network has to be designed with topology in mind from the start.

Even though the algorithm can optimize across a wide range of designs, OSPF shines when there are multiple viable network paths for any given packet transfer. This gives the algorithm more room to operate and more ability to adapt to complex traffic conditions.

All of this comes with an additional set of baggage too. OSPF is great at scaling up with networks as they add more nodes. Any time the topology changes, the routers can simply update the routing tables, and the algorithm will still do its thing.

There’s a clear and important exception to this, though. When additional routers are added, OSPF struggles with scale. Since every router carries the full topology of the network, increasing the router count significantly increases the complexity of information that the protocol has to navigate in order to function.

As a result, OSPF is useful at an enterprise scale, but when you go beyond to internet scale, it’s not a practical option.

Comparing OSPF and RIP

So far, we’ve discussed OSPF in mostly abstract terms. As a protocol and networking option, it often makes more sense to compare OSPF to another popular protocol. An obvious choice for comparison is RIP.

Routing information protocol (RIP) utilizes a concept known as distance-vector routing. OSPF focuses on finding the shortest path between nodes to manage traffic (with the ability to weigh in other factors). RIP instead optimizes traffic by hops. In other words, RIP aims to send traffic over the fewest number of hops possible.

This means that RIP would choose a longer physical routing path if it had fewer nodes along that route, and this is important for a few reasons.

First, this optimization is much simpler. In fact, RIP doesn’t even consider network paths that require more than 15 hops. Such routes are considered infinite and ignored entirely. This makes RIP much easier to design and implement as you only need to think about reducing the number of nodes between nests within the network.

Second, that simplicity comes with drawbacks. RIP can be simplistic in complex networks, and it often takes longer to resolve the fastest routes because it can’t account for weighted variables. It tunnels on hop counts, and as a result, RIP protocol is likely to send too much traffic through a single node and create bottlenecks. You can design around this issue, but as a network grows and scales, that becomes difficult.

And, that’s the real point of difference between OSPF and RIP. OSPF is great at enterprise networking; RIP is not. RIP shines in smaller and simpler networks. In such cases, its simplicity and ease of design can save time and money, but as scale becomes an issue, OSPF performs substantially better.

Use Cases for Each Protocol

Considering all of that, what are common use cases for each protocol? RIP is often deployed in small and medium businesses. It’s especially useful in networks that are not expected to grow quickly. A single branch of a major organization could operate using RIP without too much worry.

Meanwhile, OSPF shines in enterprise networking — especially when the network can operate with lower router counts. Data centers represent the prime example. Plenty of devices need to talk to each other, but you can accomplish that with more switches and fewer routers, so to speak.

OSPF is sometimes used in WANs, but those need to be WANs that see infrequent router changes. Some WAN remote monitoring and IoT applications can work for this once the network design is set and stabilized.

Ultimately, there’s a protocol for every function. OSPF is powerful and widely utilized, and now that you know more about it, you can make smart choices about network design that lead to better outcomes.

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