WHY BGP IS APPLICATION LAYER PROTOCOL

WHY BGP IS APPLICATION LAYER PROTOCOL

WHY BGP IS AN APPLICATION LAYER PROTOCOL

Many network administrators, especially those with no experience in application layer protocols, often get confused about whether BGP is an application layer protocol or not. This article will comprehensively explain why it is, in fact, an application layer protocol.

What is an Application Layer Protocol?

An application layer protocol is a set of rules that govern how applications communicate with each other. Entities in this layer are responsible for providing application-level communication services to the user. A simple analogy for this would be how people use different languages to communicate with each other. Similarly, in networking, different protocols serve as the language that machines and applications use to communicate with each other.

What is BGP?

Border Gateway Protocol (BGP) is a routing protocol used to exchange routing information among autonomous systems (AS's) on the internet. It is a path vector routing protocol, meaning that it uses information about the paths that packets have taken to reach certain destinations to calculate the best route for traffic. BGP is the de facto standard routing protocol used between AS's on the internet. It controls how data is routed around the world.

Why BGP is Considered an Application Layer Protocol

The International Organization for Standardization (ISO) defines seven layers in its networking model, and BGP undoubtedly falls under the application layer because it meets all the requirements for the layer. Here is why:

Layer 4: Transport Functions


BGP utilizes layer 4 transport protocols such as TCP and UDP to establish connections and exchange routing information between BGP speakers. The TCP or UDP port number 179 is commonly used for BGP communication.

Layer 5: Session Functions


BGP establishes sessions between peers by exchanging BGP open messages. The open message includes information about the AS number, router ID, BGP version, hold time, and optional parameters. Once the session is established, BGP peers exchange routing information using BGP update messages, which contain information about networks, path attributes, and routing policies.

Layer 6: Presentation Functions


BGP employs a specific format to represent routing information in its messages. This includes encoding and decoding techniques for encoding routing attributes, path information, and other relevant data. The BGP update messages are encapsulated within TCP or UDP segments.

Layer 7: Application Functions


BGP allows network administrators to configure routing policies that determine how routing information is exchanged and processed. These policies include route filtering, route aggregation, and route advertisement. Network administrators can use BGP to implement traffic engineering techniques to optimize the flow of traffic across their networks.

Benefits of Using BGP as an Application Layer Protocol

BGP serves as an application layer protocol to support flexible routing policies and facilitate the exchange of routing information among AS's that use different routing protocols.

Routing Policy Control


Network administrators can use BGP to implement routing policies that meet specific business requirements. These policies allow administrators to control the paths that traffic takes, prioritize certain types of traffic, and load balance traffic across multiple links.

Interoperability


BGP’s application layer nature makes it interoperable with various routing protocols used by different AS’s. This interoperability enables the seamless exchange of routing information between networks using different routing protocols.

Scalability


BGP’s design enables it to handle the large-scale routing tables required for the internet. It supports efficient routing table updates and convergence, allowing for scalable routing operations even in large and complex networks.

Conclusion

BGP is undoubtedly an application layer protocol, meeting all the requirements of the layer defined by the ISO networking model. It operates at the application layer, utilizing transport protocols, establishing sessions, employing a specific format for routing information, and allowing for the configuration of routing policies. These characteristics enable flexible routing policies, interoperability, and scalability in network routing.

Frequently Asked Questions

Q1: What are the primary functions of BGP?


BGP’s primary functions include exchanging routing information among AS’s, calculating the best paths for traffic, and facilitating the routing of traffic across the internet.

Q2: How does BGP interact with other layers of the networking model?


BGP utilizes transport protocols such as TCP or UDP at the transport layer to establish sessions and exchange routing updates. It also interacts with the network layer by determining the best paths for traffic and directing it through the network.

Q3: What are some benefits of using BGP as an application layer protocol?


BGP’s application layer nature enables flexible routing policy control, interoperability with various routing protocols, and scalability for handling large-scale routing tables.

Q4: Can BGP be used in a private network?


Yes, BGP can be used in private networks to exchange routing information between different parts of the network. However, it is primarily used for internet routing between autonomous systems.

Q5: What alternatives are there to BGP?


There are other routing protocols available, such as OSPF (Open Shortest Path First) and IS-IS (Intermediate System-to-Intermediate System), but BGP remains the standard routing protocol for internet routing.

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