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 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 blog, we will focus on the fundamental difference, i.e., BGP vs OSPF, and their basic explanation.

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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. There are several OSPF area types, all of which have been covered in a different blog.

Key Features and Characteristics of OSPF

• Link-State Protocol: It shares the state of its links with all routers in the area.
• Fast Convergence: It quickly recalculates routes when changes occur, thus minimizing downtime.
• Hierarchical Design: It uses areas to reduce overhead and improve scalability.
• Cost-Based Metrics: Chooses paths based on link cost, usually determined by bandwidth.
• Supports VLSM and CIDR: More efficient use of IP addresses compared to older protocols.
• Authentication Support: It offers MD5 and plain-text authentication for route updates.
• Multicast Routing Updates: Uses multicast instead of broadcast, conserving network bandwidth.

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.

Types of BGP

There are two types of BGP – eBGP and iBGP. Hence, BGP can be applied internally inside one AS, and externally between different ASes.

• eBGP (External BGP): Designed to allow routes to be exchanged across different autonomous systems. It is used mostly by ISPs to peer amongst themselves.
• iBGP (Internal BGP): Used to maintain those that are in the same AS to pass on BGP routes that are learned from eBGP peers.

The difference lies mainly to how the routes are sent. In eBGP, routes are generally given out to outside peers. In iBGP, one must get to a full mesh or use route reflectors to distribute internal routes.

Key Features and Characteristics of BGP

• Path Vector Protocol: BGP uses AS-path information to avoid routing loops and make informed decisions.
• Policy-Based Routing: It gives the opportunity for a network administrator to set the rules to be followed by routing and controlling the traffic using route maps and filters.
• Scalability: Efficiently manages hundreds of thousands of routes which is ideal with ISPs and large-scale enterprise networks.
• Route Aggregation: It reduces the size of the routing table by several IP prefixes to be advertised as a single one.
• Loop Prevention: Tracks each AS that a route has passed through to prevent loops.
• Incremental Updates: Only sends changes in route information, reducing bandwidth usage.
• Supports IPv4 and IPv6: Fully compatible with modern networking standards.

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 difference between OSPF and BGP.

Use Cases: When to Use OSPF vs BGP

You should use OSPF when:

• You’re working within a single organization or data center.
• You need fast convergence and dynamic routing.
• You want an easy-to-manage IGP with support for hierarchy.

You should use BGP when:

• You’re connecting to multiple ISPs (multi-homed).
• You’re involved in large-scale internet routing.
• You need more control over route selection.

Administrative Distance Comparison: BGP vs OSPF

Administrative Distance (AD) is defined to be the scale of preference which each routing protocol is assigned when talking about which one to trust with routes to given destination. The trustworthiness of the AD is directly proportional to its value.

Here’s a quick comparison:

OSPF: AD = 110

BGP (eBGP): AD = 20

BGP (iBGP): AD = 200

By this, we confirm that eBGP has the lowest AD. Thus, it is more optimal in scenarios where multiple options are present. This is more beneficial in cases where BGP and OSPF are operating simultaneously, and route redistribution is being utilized.

With that said, iBGP is usually less preferred than OSPF unless configured differently due to having a high AD of 200. In a hybrid setup, this is critical as admins may want to adjust route policies using conditions to achieve optimal routing.

Understanding AD helps network engineers avoid routing loops and ensures that the most efficient or appropriate route is chosen in multi-protocol environments.

Real-World Examples and Case Studies

Let’s look at how different organizations apply BGP and OSPF in real-world scenarios.

Example 1: An ISP Using BGP

A Tier-2 ISP peers with multiple Tier-1 ISPs and exchanges thousands of routes daily. They use BGP for:

• Inter-AS routing.
• Enforcing policies on route advertisements.
• Preventing route loops using AS-path filtering.
• Managing load balancing using local preference and MED values.

Here, BGP’s ability to scale and enforce complex routing policies is very useful to ensuring internet resilience and performance.

Example 2: An Enterprise Using OSPF

A multinational company with several regional offices uses OSPF to connect data centers and branch locations. They will be able to:

• Segment networks into multiple OSPF areas.
• Use area 0 (the backbone) to interconnect other areas.
• Implement cost-based routing to prioritize fiber links over DSL backups.
• Achieve fast failover when a router or link goes down.

In this case, OSPF’s speed, simplicity, and fault tolerance deliver high uptime and network performance without complexity.

Example 3: A Hybrid Network

An e-commerce company uses OSPF internally and BGP to connect to two ISPs. They:

• Use OSPF for LAN/WAN routing.
• Redistribute routes between BGP and OSPF carefully.
• Prefer one ISP for outbound traffic using BGP local preference.
• Monitor route updates to protect against hijacks or misconfigurations.

This hybrid approach offers the best of both: internal speed and external control.

Frequently Asked Questions

Q1. Which is better BGP or OSPF?

BGP and OSPF are both routing protocols. Both these protocols have benefits as well as some drawbacks. But, when we compare BGP vs OSPF on scalability, BGP is generally more scalable than OSPF and is also used for large networks. In terms of the preferred path, OSPF is used to determine the shortest path, while BGP is used to find the best path.

Q2. What is the difference between OSPF and BGP?

There are several difference between OSPF and BGP, but the most important is that OSPF is an intra-domain, whereas BGP is an inter-domain routing protocol.

Q3. Why OSPF is faster than BGP?

OSPF is faster than BGP in terms of convergence, which means OSPF, as compared to BGP, reacts faster to any network modifications or changes.

Q4. Is BGP a layer 3 protocol?

BGP controls the network layer (Layer 3) by operating on the Open Systems Interconnection transport layer (Layer 4).

Conclusion

OSPF and BGP are two routing protocols that differ in many aspects. Understanding the basic difference between the two will assist in choosing the best option for one’s own purposes. In this blog, we have covered the basic differences, i.e., BGP vs OSPF, as well as the basic meaning of both technologies. Join PyNet Labs’ OSPF BGP Training to learn more about these protocols.