OSPF vs. BGP: Choosing the Right Routing Protocol

Author Yana

Date 12/29/2023

Make informed decisions for your network with QSFPTEK. Explore OSPF and BGP differences, from configuration to scalability. Learn how OSPF excels in internal networks, while BGP offers scalability for larger infrastructures. QSFPTEK provides insights to optimize network efficiency by choosing the right routing protocol for your specific needs.

Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP) stand as pivotal routing protocols governing Internet traffic, providing essential guidelines for routers to determine optimal communication paths. When faced with the decision of OSPF vs. BGP, understanding the key differences is critical to choosing the appropriate routing protocol. Let's explore these differences between BGP and OSPF to help you make an informed choice.

What is OSPF Network Protocol?

Definition of OSPF in Networking

The Open Shortest Path First (OSPF) protocol, developed by the Internet Engineering Task Force (IETF), is a link-state Interior Gateway Protocol (IGP) that specializes in routing packets within a given autonomous system (AS). Open Shortest Path First operates as a link-state routing protocol, relying on detailed information about the state of network links to compute optimal route paths and make informed routing decisions. As described in RFC 2328, OSPF version 2 was designed specifically for IPv4 networks, while OSPF version 3, defined in RFC 2740, is tailored for IPv6.

The Working Principle of Open Shortest Path First Routing Protocol

The following describes the basic operating principles of the OSPF (Open Shortest Path First) protocol:

Initialization to Establish Initial Port Information:

When a router initializes or the network changes (such as link modifications or the addition/removal of routers), the relevant routers generate Link State Advertisements (LSAs). These LSAs will describe link state information.

Exchange of Link-State Information Among Routers Through Flooding Mechanism:

Routers employ a flooding mechanism to exchange LSAs. On one hand, each router sends its LSA data to all OSPF routers that are directly connected. On the other hand, routers receive LSAs from neighboring OSPF routers and update their databases accordingly.

Building a Stable Area Topology Database:

The OSPF routing protocol gradually converges through the flooding mechanism, forming a stable database representing the area's topology. At this point, each router retains a copy of this database, capturing the relationships between routers and links within the area.

Routing Table Creation:

Routers, based on their copies of the area topology database, employ a shortest path algorithm to calculate and form individual routing tables. These routing tables contain optimal paths to reach various destinations within the network, allowing routers to select the most efficient paths for data transmission dynamically.

What is the Border Gateway Protocol (BGP)?

Definition of BGP Routing Protocol

What is BGP? The Border Gateway Protocol (BGP) is a routing protocol designed to exchange Network Layer Reachability Information (NLRI) between routing domains. These domains, often called Autonomous Systems (AS), are managed independently by different administrative entities. Due to the separate control of their respective routing domains, these domains are commonly referred to as Autonomous Systems (AS). In today's Internet, a vast network of interconnected Autonomous Systems is widely used by Internet Service Providers (ISPs). The original versions, BGP-1, BGP-2, and BGP-3, were designed to exchange reachable route information between AS, establish propagation paths between AS domains, prevent routing loops, and apply routing policies at the AS level. The current and most widely used version is BGP-4.

The Working Principle of BGP in Networking

BGP operates as a standardized exterior gateway protocol facilitating the exchange of routing information among autonomous systems (AS) on the Internet. BGP routers establish peering relationships, either internal (iBGP) within the same AS or external (eBGP) with routers in different AS. Through the exchange of route advertisements, BGP routers convey information about the best paths to reach specific destinations, considering attributes such as AS path, next hop, and local preference. The protocol employs a decision process to select the optimal path based on these attributes, enabling routers to make informed routing decisions. Additionally, the BGP routing protocol supports features like route aggregation and filtering, contributing to efficient routing table management and network security.

BGP ensures the stability and scalability of the Internet's routing infrastructure. BGP features rich routing policies, and flexible route selection, and can interoperate with OSPF, IS-IS, and BFD. BGP's design promotes gradual route convergence in response to network changes, minimizing disruptions to ongoing data transmission. Despite its effectiveness, the BGP routing protocol faces security challenges, prompting the development of extensions like BGPsec to address issues such as route hijacking and enhance overall protocol security.

OSPF vs. BGP, What is the Difference?

Configuration Complexity of OSPF and BGP

Configuring OSPF and BGP involves different levels of complexity. Open Shortest Path First, being an interior gateway protocol, is typically used within an autonomous system (AS) and requires configuration of areas, routers, and link subnets. BGP routing protocol, on the other hand, is an exterior gateway protocol used for interconnecting different autonomous systems, and its configuration involves the establishment of peer relationships, route policies, and attributes. The complexity of OSPF lies in managing internal network structures, while BGP complexity is associated with inter-domain routing and policy enforcement.

Convergence Rate Differences Between BGP and OSPF

Convergence rate refers to the speed at which a routing protocol adapts to network changes. OSPF is known for its rapid convergence within an autonomous system, quickly adapting to link failures and topology changes. In contrast, BGP's convergence rate is generally slower. The slow convergence speed of BGP is because it establishes peer relationships based on the premise of IGP protocol reachability. Convergence in BGP only occurs after the underlying IGP protocol has completed its convergence.

Topological Differences Between These Two Routing Protocols

The topological differences between OSPF and BGP stem from their respective use cases. Open Shortest Path First operates within a single autonomous system, organizing the network into areas, each with its topology. This hierarchical structure allows for efficient routing within the AS. BGP, designed for interconnecting different ASs, relies on a flatter, more interconnected topology to facilitate routing between domains. Understanding these topological distinctions is crucial for network architects when choosing between OSPF and BGP.

Resource Demands of OSPF and BGP in Computer Networks

The resource demands of Open Shortest Path First and Border Gateway Protocol in computer networks vary based on their design and operational requirements. OSPF typically demands more memory and processing power within an autonomous system due to its detailed database and frequent updates. BGP, being more focused on stability in inter-domain routing, may require more bandwidth for transmitting routing information between ASs. In addition, BGP also pays attention to the scalability of the BGP routing table and imposes certain requirements on device performance.

To help you better understand the differences between OSPF and BGP, the following table shows some of the differences.

	OSPF	BGP
Gateway Protocol	Internal gateway protocol	External gateway protocol
Deployment	Easy	Complex
Convergence	Fast	Slow
Network Topology	Hierarchical	Meshed
Resource Requirements	Demanding on system memory and CPU resources	In direct correlation with the magnitude of the routing table
Protocol	IP	TCP
The Upper Limit of Network Size	Suitable for deployment in networks ranging from mid-sized to large, encompassing several hundred routers	Mainly used in MP-VPN cross-domain networks

BGP Routing Protocol vs OSPF Routing Protocol, How to Choose?

Now that we have established a foundational understanding of Open Shortest Path First and Border Gateway Protocol, the next crucial step is determining when and how to choose between these two routing protocols.

Network Type

When it comes to selecting between BGP and OSPF, one key factor to consider is the nature of the network. If your focus is on internal routings within a confined environment such as a site, company, or campus, OSPF emerges as the preferred choice. Open Shortest Path First is specifically designed for internal network routing, seamlessly facilitating communication between switches and routers within the same location.

On the contrary, if the objective is to establish connectivity between multiple sites, especially in the context of building-in sites with multiple homes, the Border Gateway Protocol becomes a more suitable option. Service providers commonly opt for BGP, leveraging its capabilities to efficiently carry customers' routes across networks.

It is important to note that OSPF and BGP are not mutually exclusive options; rather, they often complement each other in network architectures. In data center environments, Open Shortest Path First typically serves as the go-to protocol for internal routing, managing the communication between network switches and routers within the same facility. However, when data needs to traverse beyond the confines of the organization, such as connecting to an MPLS network or reaching the broader internet, Border Gateway Protocol is commonly employed to facilitate seamless communication.

In essence, the choice between OSPF and BGP hinges on the specific requirements of the network, with OSPF catering to internal communications and BGP stepping in for broader, inter-organizational connectivity.

Scale

Another crucial factor influencing the decision between Open Shortest Path First and BGP is the scale of the network. The scalability requirements of the network infrastructure play a pivotal role in determining the most suitable routing protocol.

For smaller, more contained networks, OSPF's efficiency in internal routing makes it a pragmatic choice. Its ability to manage routing within a limited geographic area ensures optimal performance in scenarios where the scale is not a significant concern.

On the other hand, as the network expands, especially when dealing with extensive interconnections and diverse locations, BGP's scalability shines through. Border Gateway Protocol is well-suited for large-scale networks, providing the flexibility and robustness required to handle complex routing scenarios across vast geographical expanses.

In summary, when choosing between OSPF and BGP, the scale of the network emerges as a critical consideration, with OSPF excelling in smaller, internal networks and BGP proving its worth in larger, more expansive infrastructures. To make it easier for you to deploy your network, I recommend the S7600 Series L3+ Switches, which support both OSPF and BGP.

Conclusion

In summary, when choosing between Open Shortest Path First and Border Gateway Protocol, consider their different strengths. The OSPF routing protocol provides fast internal communication within autonomous systems, suitable for smaller networks, while the BGP routing protocol prioritizes scalability and stability for larger, interconnected infrastructures. The choice depends on factors such as network size, type, and topology. Striking a balance between the efficiency of OSPF and the scalability of BGP ensures a customized routing solution that meets the specific needs of the network.