Exterior Gateway Protocols: Connecting Autonomous Systems

🤝 Introduction

Exterior gateway protocols (EGPs) are essential for communication between routers representing the edges of different autonomous systems (ASs). Unlike interior gateway protocols (IGPs) used within a single AS, EGPs facilitate information exchange across organizational boundaries. These protocols are crucial for the internet's operation, enabling data to flow seamlessly between independent networks.

🌎 The Internet: A Mesh of Autonomous Systems

The internet is a vast interconnected web of ASs, each managed by a single organization. Core internet routers need to know about these ASs to properly route traffic. Their primary goal is to deliver data to the edge router of an AS, as ASs are defined collections of networks.

🏢 IANA: Managing the Internet's Infrastructure

The Internet Assigned Numbers Authority (IANA) is a non-profit organization responsible for managing critical internet infrastructure, including IP address allocation. Without a central authority like IANA, the internet would descend into chaos, as anyone could claim and use any IP space they desired.

🔢 ASNs: Identifying Autonomous Systems

Along with managing IP address allocation, IANA also assigns Autonomous System Numbers (ASNs) to individual ASs. ASNs are 32-bit numbers, similar to IP addresses, but typically represented as a single decimal number. This difference stems from two key factors:

1. IP addresses: Need to represent both network ID and host ID portions, which is easier with four 8-bit sections (especially in the era of address classes).

2. ASNs: Rarely change to accommodate more networks or hosts. Only core internet routing tables need updates to reflect changes in ASN representation.

3. Human readability: ASNs are less frequently viewed by humans compared to IP addresses. While knowing that the IP address 9.100.100.100 belongs to the 9.0.0.0/8 address space owned by IBM is useful, simply knowing that AS19604 belongs to IBM is sufficient for most purposes.

🔭 Understanding EGPs: Beyond the Scope for Most IT Professionals

Unless you work for an internet service provider, delving into the intricate details of EGPs is likely unnecessary for most IT professionals. However, grasping the fundamentals of ASs, ASNs, and how core internet routers route traffic between them is crucial for understanding the internet's basic building blocks.

💡 Conclusion

EGPs play a vital role in connecting autonomous systems and ensuring seamless data flow across the internet. Understanding the concepts of ASs, ASNs, and IANA's role in managing internet infrastructure provides a deeper appreciation for the internet's underlying architecture.