Open Shortest Path First (OSPF): Why do we need it?

Many routing protocols in the networking domain define a set of rules on how data should be transmitted. Open Shortest Path First (OSPF) is one such dynamic routing protocol. It is called a dynamic protocol as it can dynamically exchange routing information between the routers that are the nearest neighbors. In this blog, we will learn what the OSPF protocol is and how it works. We will also learn about the different states of the OSPF protocol. In the end, we will also discuss the advantages and disadvantages of the protocol.

What is Open Shortest Path First (OSPF)?

OSPF, short for Open Shortest Path First, is a dynamic routing protocol commonly used in large-scale IP networks. It functions by determining the shortest path to route data packets between routers. OSPF calculates this path based on various metrics such as link bandwidth, delay, and cost.

At its heart, OSPF is a routing protocol built for Internet Protocol (IP) networks. It operates within an Autonomous System (AS) — a collection of IP networks and routers under the control of one entity that presents a common routing policy to the Internet.

How does OSPF work?

Two important concepts in Open Shortest Path First are areas and neighbors.

• Areas are groups of routers in an AS, essentially forming a collection of zones with logical boundaries. Areas are typically identified with a number. Area 0 is always the backbone, to which all other areas connect.
• OSPF-enabled routers in the same area establish “neighbor” relationships using a HELLO packet to exchange routing information.
  In OSPF, the routers do not need to send the entire routing table to neighboring routers every few seconds. Instead, information is sent only when a change has taken place.

When an OSPF router in a given area of the AS that learns of a routing table change or detects a change in the network immediately multicasts the information to all other OSPF-enabled nodes in the area. Multicasting is a way to ensure every router in that area has the same information about the AS topology, a concept known as flooding. This information is used to calculate the best end-to-end path to the eventual destination in the AS.

Notably, the multicast contains only the latest update. Routing tables can be incredibly large, and retransmitting them in full every time can degrade network performance. When routes change — which can occur due to equipment failure or the addition of new devices — the time it takes OSPF routers to reconcile these changes and identify the best new, loop-free path between endpoints is called convergence time.

Why do we need it?

• Open Shortest Path First protocol is versatile, supporting both IPv4 and IPv6 network architectures.
• It efficiently distributes network traffic to prevent overload by employing load-balancing techniques.
• The protocol employs an algorithm that ensures the network remains free of routing loops.
• Due to its open-standard nature, OSPF is compatible with a wide array of routers, not limited to any single manufacturer.
• It operates without class-based restrictions, offering flexibility in defining networks.
• OSPF boasts an unrestricted number of router hops within its reach.
• The protocol excels in quickly establishing and updating routing information across the network.

Benefits of using Open Shortest Path First

Using OSPF in network design offers multiple benefits, particularly for medium to large-sized networks:

• Scalability: Open Shortest Path First is highly scalable and supports large, complex networks by breaking them into smaller, more manageable areas. It can handle thousands of routers, making it suitable for enterprise environments and ISPs.
• Efficient Use of Network Resources: OSPF calculates the best path based on metrics such as bandwidth, delay, and cost, ensuring optimal use of available network resources. This leads to improved performance and reduced latency.
• Rapid Convergence: OSPF’s ability to rapidly converge during network changes ensures minimal disruption to network services, making it ideal for mission-critical environments where downtime is unacceptable.
• Load Balancing and Redundancy: With its support for equal-cost multi-path routing, OSPF allows for redundancy and efficient load distribution across multiple network links, reducing the likelihood of congestion and improving reliability.
• Interoperability: OSPF is an open standard, which means it can interoperate with routers from different vendors, unlike proprietary protocols like Cisco’s Enhanced Interior Gateway Routing Protocol (EIGRP).
• Security: The use of authentication ensures that only trusted routers exchange routing information, safeguarding the network from unauthorized devices.

The disadvantages of OSPF

The following are the disadvantages of the Open Shortest Path First protocol:

• It needs extra storage. Therefore, it means that it needs an extra CPU process to run the SPF algorithm.
• It needs more RAM to save adjacency topology.
• It is very complex. Therefore, it’s very difficult to troubleshoot.

Conclusion

OSPF is a powerful and flexible routing protocol that can be used to design and build large and complex networks. OSPF uses a link-state routing algorithm that computes the shortest path to each destination based on the OSPF cost of each link.

OSPF allows dividing the network into areas and choosing different types of areas and border routers to optimize routing performance and efficiency. OSPF also supports authentication, VLSM, route summarization, and redistribution to enhance security and scalability.