Learn what OSPF is, a reliable link-state routing protocol for IP networks. Discover how OSPF works, its advantages, and how it can be used to optimize your network connectivity.
In a computer network, connection is an important function. In creating a good connection in a network, a routing protocol is needed that functions to determine how a router communicates and chooses the best route between two nodes in a computer network.
Routing is the process of selecting a path that will be passed by a data packet in a computer network. There are various types of routing protocols, one of which is open shortest path first (OSPF). OSPF is a routing protocol that uses a link state-based routing algorithm. OSPF falls into the Interior Gateway Protocol (IGP) category and can work on a company’s internal network.
The OSPF protocol is very commonly used by networks in large companies. OSPF does not use TCP/IP transport protocols such as UDP or TCP but encapsulates data in IP datagrams. This article will discuss in more detail about OSPF starting from the definition, history, function, how it works, types and advantages and disadvantages.
Understanding OSPF
OSPF (Open Shortest Path First) is an interior routing protocol used in computer networks. OSPF is a protocol that implements link-state to calculate the shortest path between two nodes in a network based on available network topology information. This protocol is used in IP-based networks and is often used in larger networks such as Internet Service Providers (ISPs) or complex corporate networks.
OSPF uses the Dijkstra algorithm, where OSPF routing is able to calculate the shortest path and consider factors such as link speed, network load, and other metrics in making routing decisions. OSPF uses a link-state database called the OSPF Link-State Database (LSDB) to store information about network topology and uses the SPF (Shortest Path First) algorithm to calculate the shortest path to the destination.
OSPF is a type of Dynamic Routing , which is a routing method in which routers automatically learn and determine paths in the network by using certain routing algorithms and sharing information between routers.
History of OSPF
The OSPF (Open Shortest Path First) protocol was developed by the IETF (Internet Engineering Task Force) as an interior routing protocol for IP networks . The history of OSPF began in the early 1980s when there was a need to replace the existing routing protocol at that time, namely RIP (Routing Information Protocol), OSPF uses the Dijkstra algorithm, OSPF routing is able to calculate the shortest path and consider factors such as link speed, network load, and other metrics in making routing decisions. OSPF uses a link-state database called the OSPF Link-State Database (LSDB) to store information about network topology and uses the SPF (Shortest Path First) algorithm to calculate the shortest path to the destination. OSPF is a protocol that has several limitations in managing large and complex networks.
In 1987, the first version of OSPF was published as an IETF standard in RFC 1131. This early version of OSPF was designed to work on IPv4 networks and used link-state routing methods to calculate the shortest path between any two nodes in the network. OSPF also adopted some concepts from earlier link-state routing protocols, such as IS-IS (Intermediate System to Intermediate System).
Over time, OSPF continued to develop and improve. In 1990, OSPF version 2 was introduced in RFC 1247, which added several new features such as support for CIDR (Classless Inter-Domain Routing) subnetting, OSPF message authentication, and several other changes.
Later, in 1998, OSPF version 3 was introduced in RFC 2740 in response to the introduction of the IPv6 protocol. OSPF version 3 was designed to support IPv6-based networks while retaining many of the features and concepts of previous OSPF versions.
Since then, OSPF has continued to improve and develop. Several revisions and minor changes have been made to improve the efficiency and security of OSPF, including the addition of new features such as MPLS (Multiprotocol Label Switching) and integration with other protocols such as BGP (Border Gateway Protocol).
To this day, OSPF remains one of the most commonly used interior routing protocols in IP networks, especially in complex and large networks such as ISP (Internet Service Provider) and corporate networks.
OSPF Functions
OSPF (Open Shortest Path First) has several main functions in computer networks, namely:
Routing Interior
OSPF is used as an interior routing protocol responsible for managing the delivery of data packets within an autonomous system (AS) or local area network. OSPF calculates the shortest path between two nodes based on available network topology information, considering factors such as link speed and network load. The main function of OSPF is to determine the best path to deliver data packets between source and destination nodes in a network.
Automatic Recovery
OSPF supports automatic recovery in the event of a link failure or topology change in the network. When a change occurs, OSPF automatically recalculates the shortest available path and sends routing change information to all nodes in the network. This allows the network to continue operating and redirect traffic to available paths.
Area Division
OSPF allows the network to be divided into smaller areas to reduce routing complexity and overhead. By dividing areas, OSPF can group interconnected nodes into separate areas and use routing summaries to reduce the amount of routing information that must be exchanged between areas. This improves network efficiency and scalability.
Redistribution Routing
OSPF supports routing redistribution, which is the process of incorporating routing information from other routing protocols into OSPF. This allows OSPF to communicate with other routing protocols used in the network and incorporate the routing information obtained from those protocols into the OSPF routing table. With routing redistribution, OSPF can interoperate with other routing protocols and expand the network coverage.
Security
OSPF has several security features that allow routing information to be secured within a network. For example, OSPF supports OSPF message authentication, which ensures that received routing messages come from a trusted source and have not been manipulated. In addition, OSPF can use backbone areas to isolate sensitive areas of the network and enforce special security policies.
With the above functions, OSPF helps organize and manage network traffic efficiently, ensures optimal delivery of data packets, and provides automatic recovery capabilities in the event of disruptions or changes in the network.
How OSPF Works
Here are the general steps on how OSPF (Open Shortest Path First) works in a computer network:
OSPF Router Identification and Configuration
On each Router in the network that will use OSPF, you need to identify the network interfaces that will participate in OSPF and configure them as part of the OSPF area.
Hello Packet Delivery
Each OSPF router sends a “Hello Packet” through its configured OSPF interface. Hello Packets are used to establish and maintain connections with OSPF neighbors.
Form Adjacency
Each OSPF Router receives Hello Packets from OSPF neighbors through the same interface. If the neighbor’s OSPF configuration is considered valid, the router will form an adjacency with that neighbor. An adjacency is a relationship formed between two OSPF routers to exchange topology information.
Link-State Database (LSDB) Exchange
Once an adjacency is established, OSPF routers will exchange Link-State Databases (LSDB). Each router sends a Link-State Advertisement (LSA) containing its local network topology information. This LSA will be stored in the LSDB database of each OSPF router.
Shortest Path Calculation
Once all OSPF routers have exchanged topology information and have an up-to-date LSDB database, each router will use Dijkstra’s algorithm to calculate the shortest path to all destinations in the network. The results of this calculation will be stored in the OSPF routing table.
Routing Update Distribution
OSPF routers will broadcast routing update information to OSPF neighbors using OSPF messages, which contain information about the shortest path to a specific destination. These OSPF messages will be forwarded by neighboring routers to other neighbors until the entire OSPF network receives the routing update information.
Maintenance and Restoration
OSPF continuously monitors the network state to detect topology changes or failures. If a change occurs, OSPF will update the LSDB database, recalculate the shortest path, and send routing updates throughout the network to ensure optimal delivery of data packets.
With the above working method, OSPF allows routers in the network to exchange topology information, calculate shortest paths, and maintain up-to-date routing tables. This allows OSPF to manage data packet delivery efficiently and provide automatic recovery capabilities in the event of a network outage.
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Advantages and Disadvantages of OSPF
There are some advantages and disadvantages of OSPF in the following network some advantages and disadvantages of OSPF routing protocol
Advantage
Scalability
OSPF is designed to manage large and complex networks. By dividing the area, OSPF allows the network to be grouped into smaller areas, reducing complexity and routing overhead. This makes OSPF highly scalable and can handle growing networks well.
Convergence Speed
OSPF uses Dijkstra’s algorithm which is efficient in calculating the shortest path. When a topology change or failure occurs, OSPF quickly recalculates the shortest path and propagates routing information throughout the network. This reduces convergence time, so traffic can be quickly rerouted to alternative paths.
Automatic Recovery
OSPF has strong auto-healing capabilities. If a topology change or link or router failure occurs, OSPF will automatically detect the change and recalculate the shortest path. This allows the network to recover quickly without requiring manual intervention.
Traffic Engineering
OSPF supports more complex traffic engineering settings in a network. Through the use of areas and the ability to set metrics, OSPF allows network administrators to direct traffic specifically through desired paths. This provides better control over the delivery of data packets in the network.
Security
OSPF has strong security features. With OSPF message authentication, only routers that have valid authentication can participate in OSPF. This helps protect the network from spoofing attacks or unauthorized manipulation of routing information.
Support for IPv6
OSPF supports IPv6 , the next generation internet protocol. This allows OSPF to be used in networks that use IPv6 as the primary communication protocol.
Deficiencies
Configuration Complexity
OSPF configuration can be complicated, especially in large, complex networks. Network administrators need to understand OSPF concepts, including area division, metric settings, and OSPF neighbor configuration. Misconfigurations can cause serious routing problems.
High Memory and Processor Usage
OSPF requires significant resources in terms of memory and processing usage. Routers running OSPF must have enough memory to store the Link-State Database (LSDB) and enough processing power to perform shortest path calculations efficiently. This can be a problem in very large networks or with limited hardware.
Increased Network Overhead
OSPF sends hello packets periodically to maintain connections and maintain adjacency with OSPF neighbors. This can cause increased network overhead, especially in networks with a large number of routers. Increased hello packet traffic can affect overall network performance.
Slow Convergence on Large Networks
While OSPF has good convergence speed in small to medium networks, in very large networks with thousands of routers, OSPF convergence can take much longer. The process of recalculating the shortest path and propagating routing information throughout the network can take significant time.
Depends on Transport Protocol
OSPF relies on a reliable transport protocol, such as IP, to send OSPF messages between routers. If the transport protocol experiences problems or is disconnected, then OSPF will also be affected. Therefore, the stability and reliability of the transport protocol are very important in the operation of OSPF.
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OSPF Types
OSPF (Open Shortest Path First) has several different types, depending on its role and function in the network. Here are some common OSPF types:
OSPF Internal (OSPFv2)
This is the most commonly used type of OSPF. Internal OSPF is used for interior routing within a single network. OSPFv2 uses IPv4 as the primary communication protocol and has wide support in network devices.
OSPFv3
OSPFv3 is a version of OSPF designed to support IPv6 routing. OSPFv3 is used to manage IPv6 interior routing in IPv6-enabled networks. It has similar features and characteristics to OSPFv2, but uses IPv6 message formats and addresses.
OSPF NSSA (Not-So-Stubby Area)
OSPF NSSA is a type of OSPF used in NSSA areas. NSSA areas are OSPF areas that have hybrid characteristics between stub areas and normal areas. OSPF NSSA allows the use of external routes (routes from outside the area) into the NSSA area, but does not allow external routes to be propagated into the normal area.
OSPF Stub Area
OSPF Stub Area is a type of OSPF used in stub areas. A stub area is an OSPF area that has one or more default routes to a normal or backbone area. In OSPF Stub Area, routers in the stub area only have default route information and internal topology information. External routes are not propagated within the stub area.
OSPF Totally Stubby Area
OSPF Totally Stubby Area is a type of OSPF used in totally stub areas. Totally stub areas are a more restrictive variant of stub areas. In OSPF Totally Stubby Area, in addition to external routes, all summary routes from the backbone are also ignored. Routers in a totally stub area only have default route information and internal routes to other areas.
OSPF Virtual Link
OSPF Virtual Link is used to connect two physically separated OSPF areas through another OSPF area network. Virtual Link is used when there is no direct path between the two OSPF areas that you want to connect. Virtual Link allows traffic to pass through another OSPF area to reach its final destination.
Each of these OSPF types has its own purpose and uses in network management. Selecting the right OSPF type depends on the needs and characteristics of the network being implemented.
Conclusion
What is OSPF? OSPF is a routing protocol that offers a scalable, fast, and secure solution for managing data traffic in a network. OSPF is the primary choice for organizations that require efficiency in managing large and complex networks. With clear functions, advantages, and how it works, OSPF routing becomes a vital element in modern network architecture.
Reference
Musril, HA (2017). Application of Open Shortest Path First (OSPF) to Determine the Best Path in a Network . Applied Electrical Telecommunication Journal, July 2017. Department of Informatics and Computer Engineering Education (PTIK), State Islamic Institute (IAIN) Bukittinggi.
Shi, H., Wang, Y., & Zhang, R. (2015). Study on OSPF Routing Protocol of Computer Network Based on Packet Tracer. 3rd International Conference on Management, Education, Information and Control (MEICI 2015). School of Computer and Information Engineering, Beijing University of Agriculture, China.
Author: Hassan Rizky Putra Sailellah | Editor: Meilina Eka Ayuningtyas
