What is OSPF? | Exploring Open Shortest Path First Protocol

In today’s world, networks are super crucial for communication, and routing protocols are vital to making sure data gets where it needs to go. OSPF (Open Shortest Path First) is one of these protocols, and it’s trendy. It helps routers figure out the best way to send data around a network. In this article, we’ll learn all about what OSPF is—how it works, what it can do, and how it makes networks better.

We’ll also check out how the OSPF protocol compares to other routing protocols and why it’s good for security, handling lots of traffic, and keeping everything balanced. So, if you want to know more about how computers chat effectively on networks, stick around!

What is the OSPF Protocol?

Credit: CiscoPress

Understanding OSPF: How Computers Talk Effectively on Networks

OSPF (Open Shortest Path First) is a style of routing protocol used inside networks. It helps routers figure out the best way to send data around. It uses a method called the Dijkstra link-state algorithm to find these paths. Instead of distance, it looks at “cost” to decide which path is best. It also makes sure all routers in a LAN know about the same things, which helps everything run smoothly.

Also, it is a type of routing developed by experts to improve how networks work. It was made because the old way, called RIP version 1, had some problems:

  1. It was slow to react when things changed in the network.
  2. It only measured the distance between points.
  3. It could only spread traffic across multiple paths if one were relaxed.
  4. It couldn’t tell apart different kinds of services.
  5. It couldn’t tell the difference between hosts, routers, and types of networks in the same system.

Some issues were fixed with RIP version 2. It added more ways to measure things and supports subnet routing and sending messages to multiple places at once. However, the OSPF protocol, which experts make, works differently. It’s a standard way for computers to find the shortest route between two points on a LAN.

What are the OSPF ProtocolFeatures?

1. Quick Response Without Loops to Changes

The SPF algorithm that it uses is way faster than the one used by RIP. It helps routers figure out routes through a network much quicker.

Also, every device on the network calculates the map in the same way. This means they all have the same map, which helps avoid creating loops or getting stuck counting nodes forever. This is a big issue with protocols like RIP, which use distance vector algorithms.

2. Security Against Changes

For the routing algorithm to do its job right, every network node needs to have the same picture of the LAN setup. If there are any mess-ups, like errors in syncing or too much info flooding the system, it can cause problems.

It says all the talk between routers needs to be checked to make sure it’s coming from trusted sources. There are different ways to prevent it, and you can pick different ways for other parts of the LAN. The whole point is only to let the good routers share info about routes.

3. Support for Multiple Measurements

With today’s tech, we can handle lots of measurements at once. When we’re figuring out the best path between two points, we can consider different factors. Each factor might give us a different “best” route. Depending on what we need for communication, we can choose which measurements to focus on.

  • Higher performance
  • Low latency
  • Lower costs
  • Increased reliability

Being able to use different measurements to find a route means that once OSPF picks a metric and makes a path, it always follows that same path for the same type of data.

4. Load Balancing in Multiple Ways

The OSPF protocol lets us balance the load between nodes by using multiple paths. This is how we do the balancing:

  • A tweaked SPF version stops making incomplete loops.
  • An algorithm figures out how much traffic should go on each road.
  • It can handle adding more outside routes as things grow.

OSPF’s Basic Show Commands

If you want to check if the OSPF protocol is doing its job right on your device, you can use special commands to do it. These commands will show you info and stats about how this protocol is doing on your device so you can see if everything’s running smoothly.

Router# show ip ospf
Router# show ip ospf neighbor
Router# show ip ospf interface
Router# show ip route ospf
Comparison of OSPF Show Commands
AspectOSPF CommandDescription
View Databaseshow ip ospf databaseThis command shows the OSPF database. It gives lots of details about the routes in the network and where they come from.
External Border Routersshow ip ospf border-routersThis command shows routers called ASBRs in the network. They’re special because they connect to networks outside of this protocol.
Virtual Linksshow ip ospf virtual-linksThis command shows virtual links in the network. They’re used when there are many different areas in the network.
Statisticsshow ip ospf statisticsThis command gives you numbers and details about this protocol, like how many packets are sent and other important stuff to check how well it is working.
Eventsshow ip ospf eventsThis command shows its events. It tells you about any changes or important things that happen in the LAN.
External Routesshow ip ospf database externalThis command displays routes that come from outside OSPF and are added using ASBRs.
The Routing Tableshow ip ospf routeThis command shows routes in the routing table. It tells you about routes in the network and where they came from.

How Exactly Does OSPF Work?

Here’s what OSPF routers do step by step:

  • They find their neighbors.
  • They pick a Designed Router (DR).
  • They sync up their databases.
  • They figure out the best routes.
  • They keep track of connection status.

The routers do all these things when they start up and whenever something happens on the LAN. Every router has to go through these steps for each node it’s connected to, except for calculating the routing table. Each router keeps one routing table that includes all the LANs.

OSPF Protocol Messages

There are five kinds of messages in this protocol.

  1. HELLO Message
  • It figures out who its neighbors are to make a map.
  • It tells other routers about its map to keep it safe.
  • It picks a particular router for the multicast network.
  • It finds out who the main router is right now.
  1. Database Description

The router shares info to fill in any missing data when two nodes first connect or sync up.

  1. Link Status Request

It’s like asking for any info that’s not in a router’s database or has yet to be shared when two routers are talking to each other.

  1. Link Status Update

Link status is used to reply to request messages and automatically tell when there are changes in the network setup.

  1. ACK Link Status

It’s like saying “receipt” when you receive an update about the status of a link.

Open Shortest Path First Package Content

This protocol creates packets with these parts:

  • Version Number: Shows which protocol version is used.
  • Type: Tells what kind of packet it is (like Hello, database status, or connection request).
  • Packet Length: This shows how big the packet is, including the header.
  • Router ID: Says where the packet is coming from.
  • Area ID: Shows which area the data belongs to; all OSPF packets are part of an area.
  • Checksum: Makes sure the packet has been fixed.
  • Authentication Type: Tells what kind of security is used for authentication.
  • Authentication Data: Has the info needed to check if the packet is legit.
  • Data: Holds the main info being sent.

The OSPF protocol is prevalent for extensive LANs. You can make it safer by using MD5 (Message-Digest Algorithm 5, a robust encryption method) to check your data before switching routes or accepting connection updates.

Also, VLANs are a way to split up a network into smaller parts for better management. They’re closely linked with dynamic routing protocols like OSPF. These groups help organize the LAN, so routing protocols like OSPF can let different parts of the LAN talk to each other and send data where it needs to go. If you want to learn more, read our article on what VLAN is.


In short, the OSPF protocol in networking is essential for getting data where it needs to go in a LAN. It’s faster, safer, and can handle lots of different tasks compared to other protocols. It’s great for spreading out the work between devices and dealing with a ton of traffic.

Plus, it gives us special commands to check how things are going and messages to keep everything working right. Overall, it is a big help in making sure computers can talk to each other quickly and efficiently on a network.

If you want to learn more about routing methods like OSPF, you might like our article about what EIGRP is. It’s a well-liked method known for being fast and not using up too much network space. If you understand both OSPF and EIGRP, you can decide which one is best for your LAN.

Copyright © 2018 - 2024