BGP vs OSPF – What’s the difference?

Introduction

Using routing protocols, routers may automatically and dynamically exchange routing data. As each routing protocol has been developed to be ideally suited to a certain network implementation situation, there are several routing protocols to select from, each with its own advantages and disadvantages. Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP) are two of the most widely utilized routing protocols in use today. But the question that arises is which one is better. In this article, we will focus on the fundamental difference, i.e., BGP vs OSPF, and their basic explanation.

Let’s begin with the basic difference between OSPF and BGP.

BGP vs OSPF

The main difference between OSPF and BGP is that OSPF is an Interior Gateway Protocol (IGP) used within an autonomous system, primarily focusing on efficient routing within a single network, whereas, BGP is an Exterior Gateway Protocol (EGP) that facilitates routing between different autonomous systems on the internet, prioritizing inter-domain routing and policy-based decision-making. Below we have compared some of the factors of these two protocols.

We have explained the fundamental difference between the two; let’s now understand what OSPF and BGP really are.

What is OSPF?

A single Autonomous System (AS) may route packets using the internal gateway protocol (IGP) OSPF. OSPF is a link-state routing protocol, in contrast to other IGPs. In other words, it makes routing choices and calculates route pathways using link-state information.

After the beginning of the protocol, each router running OSPF broadcasts link-state advertisements (LSAs) providing details about its connected interfaces and routing metrics across the AS or area. All of the routers in the area get any changes made to any one of the routers. Such an update triggers a repeat of the shortest-path-first algorithm.

Each AS is divided into smaller groups termed areas by OSPF. The LSA databases on each router in a given area are identical. The information regarding the other areas has also been summarized.

Advantages of OSPF

Here are some advantages of OSPF –

• OSPF is an open standard protocol, and it works on many routers.
• OSPF provides a loop-free topology with the SPF algorithm.
• OSPF provides fast convergence through both triggered updates and incremental updates.
• OSPF supports VLSM and route summarization for hierarchical designs.
• OSPF supports both versions of the IP protocol. OSPFv2 supports IPv4 and OSPFv3 supports IPv6.
• OSPF uses load balancing with equal-cost routes to the same destination.
• OSPF support all sizes of networks.

Disadvantages of OSPF

Some disadvantages of OSPF are –

• OSPF needs more information to calculate the finest route to every destination.
• OSPF requires more memory storage in comparison to other routing protocols.
• OSPF requires additional CPU processing as it operates the SPF algorithm to calculate the finest route.
• OSPF requires experienced network managers who can configure it because it is difficult to configure and troubleshoot.

What is BGP?

BGP or Border Gateway Protocol is a type of external gateway protocol (EGP). BGP is a routing protocol that is mainly used for inter-domain routing. But BGP may also be configured to advertise networks inside an AS and, when doing so, can perform similarly to IGPs.

To communicate routing data between routers in the same AS or other ASs, BGP is utilized. A group of routers operating under one administrative authority is known as an AS. The path leading to a destination is an AS path. It also includes a list of the ASs that the route travels through in order to get to a certain router. Additional data is attached to each route in the form of path attributes. In order to modify how the router routes the traffic, routing policies make use of the path attributes.

Advantages of BGP

Some advantages of BGP –

• BGP can be implemented on a large scale.
• BGP improves the efficiency of routing.
• BGP avoids loops if multiple physical links exist.
• BGP is a very important and scalable routing protocol.
• BGP can easily fix the count-to-infinity problem.
• BGP reduces the size of the Internet routing table because it uses CIDR.

Disadvantages of BGP

Here are the same disadvantages of BGP –

• BGP is difficult to configure and maintain.
• BGP may affect network instability.
• BGP convergence time is slow.
• BGP lacks internal security measures.
• BGP is not suitable for small networks.

We now have a basic understanding of OSPF and BGP. Let’s now understand the difference between the two, i.e., BGP vs OSPF, in detail.

Difference between OSPF and BGP

OSPF and BGP are two routing protocols that are used to exchange information between routers in a network. They differ on the basis of several factors, such as:

Function

OSPF: It is mainly used for intra-domain routing, i.e., within the same domain or AS.

BGP: It is mainly used for inter-domain routing, i.e., between different domains or ASes.

Gateway Protocol

OSPF: Being an inner gateway protocol (IGP), OSPF may only be used in networks that are part of a single autonomous system (AS).

BGP: As an external gateway protocol (EGP), BGP communicates with other independent systems or networks that are run by different administrations.

Implementation

OSPF: These are generally easier to implement and configure as compared to BGP. Now, the question that arises is why OSPF are easier to implement. The reason behind this is it uses link-state routing and automatically discovers neighbors as well as adjacencies.

BGP: These are complex and require manual configuration of peers as well as policies. The reason behind this is it uses path-vector routing and relies heavily on TCP for reliable communication.

Convergence

OSPF: It converges faster than BGP. The reason behind this is it uses flooding to propagate link-state updates, and whenever there is an update or modification in the network topology, it triggers updates.

BGP: As compared to OSPF, BGP converges slower. The reason behind this is it uses incremental updates and applies filters in order to choose the best path for each destination.

Need for device resources

OSPF: As it keeps a link-state database for each region and uses the Dijkstra algorithm to find the shortest route, OSPF uses more device resources than BGP.

BGP: As it maintains a routing table with the optimal route for each destination and employs a straightforward path selection method, BGP requires fewer device resources than OSPF.

Algorithm Used

OSPF: It uses the Dijkstra algorithm, which is a shortest-path-first algorithm. It is mainly used for finding the least-cost path in a network.

BGP: In the case of BGP, it uses the Bellman-Ford algorithm, which is mainly a distance-vector algorithm that finds the shortest or lowest-cost path in a network.

These are the major differences between OSPF and BGP.

Hope this helps you to understand the OSPF and BGP better!

To get a better understanding and in-depth knowledge of these routing protocols, you can enroll in our Routing Protocol combo training (OSPF+BGP), which is starting on 30th November at 1 PM IST/ 2:30 AM EST.

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