An Introduction to BGP: Border Gateway Protocol Explained

Welcome to the world of networking and the Border Gateway Protocol, commonly known as BGP. In this lesson, we will embark on a journey to understand the fundamental components of BGP, an essential protocol that forms the backbone of the internet’s routing infrastructure.

What is Border Gateway Protocol (BGP)?

At its core, BGP is an exterior routing protocol. But what does that mean? To grasp this, we must first differentiate between interior and exterior routing protocols.

  • Interior Routing Protocols: These are used within an organization, typically within a single autonomous system (AS). Examples include RIP (Routing Information Protocol) and OSPF (Open Shortest Path First). They’re designed for routing within LAN environments.
  • Exterior Routing Protocols: BGP falls into this category. Exterior routing protocols are used to share route availability information between different autonomous systems. Autonomous systems are networks under the control of a single administrative entity, and they may employ their own routing protocols and policies.

Key BGP Concepts

Now, let’s delve into some key concepts and components of BGP:

  1. Manual Prefix Sharing: In BGP, routes to available networks (prefixes) are not automatically shared. Each BGP router must be manually configured to exchange route information with its peers.
  2. BGP Peering: To establish BGP communication between routers in different autonomous systems, both routers need to be configured with each other’s IP addresses and authentication information. This coordination ensures successful peering.
  3. Route Selection Logic: BGP routers often have multiple prefixes pointing to the same destination network. However, only one prefix can be advertised by the BGP protocol. BGP uses a built-in sequence of logic to determine the best route, considering factors like AS path length and attributes.
  4. TCP Port 179: BGP communicates over TCP port 179. This is crucial because, if BGP routers are behind firewalls, the firewall must allow traffic on this port for BGP communication to occur.
  5. Autonomous Systems: In the world of BGP, networks are organized into autonomous systems (ASes), each identified by an autonomous system number (ASN). ASN is essential when configuring BGP routers, as it designates the AS to which the router belongs.
  6. EBGP and IBGP: BGP routers can form pairings over two types of connections:
    • EBGP (External BGP): This type of peering happens between routers in different autonomous systems. It’s often used for inter-domain routing.
    • IBGP (Internal BGP): IBGP peering takes place within the same autonomous system. While the rules are somewhat different for IBGP, it’s crucial for internal routing within an AS.

The Global Scale of BGP

To appreciate the scale of BGP, consider that the internet is divided into numerous autonomous systems. Each AS is a network operated by an entity (e.g., a company or an ISP) with its own routing policies. These ASes peer with one another using BGP, forming the complex web of the internet’s routing infrastructure.

  • Iceland, a small example, has 62 registered ASNs and 68 visible pairings.
  • The United States, a larger example, has nearly 17,000 ASNs and almost 25,000 visible pairings.
  • Globally, there are over 63,000 IPv4 autonomous systems (as of January 2019).

BGP is the protocol that enables these networks to communicate with each other effectively and efficiently.

BGP in AWS Hybrid Networks

In AWS hybrid networks, BGP plays a significant role. Direct Connect connections always use BGP for dynamic routing, and VPNs can also be configured for dynamic routing with BGP. Whether you’re connecting to AWS via Direct Connect or VPN, BGP is the driving force behind route propagation.

In conclusion, BGP is a vital routing protocol that facilitates communication between autonomous systems, forming the backbone of the internet. Understanding BGP is crucial for network administrators and cloud professionals working with AWS or any network that spans multiple autonomous systems.

Stay tuned for more lessons on BGP as we explore its intricacies and practical applications in greater detail. Thank you for joining us in this introduction to BGP!

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top