BGP.KMCD.DEV
Global Routing Telemetry
Understanding BGP
The Postal Service of the Web
The Border Gateway Protocol (BGP) is the routing protocol of the internet. It acts like the postal service for the web, allowing different networks (Autonomous Systems or ASes) to announce which IP addresses they control and discover the most efficient paths to send data to each other. Because BGP relies on trust, it is vulnerable to misconfigurations or malicious attacks known as Route Hijacks.
IP Prefixes & Subnetting
In BGP, we don't route individual IPs, but Prefixes (blocks of addresses). A prefix like 192.0.2.0/24 represents 256 addresses.
- Specific (/24): A "small" prefix. BGP always prefers the most specific route. A hijacker announcing a /24 can "steal" traffic from a larger /23 announcement.
- Aggregate (/8): A "large" prefix covering millions of IPs. Used to keep the global routing table manageable.
Autonomous System (AS)
A large network or group of networks under a single administrative control. Every major entity on the internet (Google, Comcast, CERN) is assigned a unique ASN to identify itself in the global BGP table.
Peering vs Transit
Peering is a direct, usually free connection between ASes to exchange traffic. Transit is when a smaller AS pays a larger provider to carry its traffic to the rest of the global internet.
BGP Sessions & Peering
Two ASes establish a Session to exchange routing information. This "peering" is the handshake that allows data to flow across the boundaries of different corporate and national networks.
The Global Routing Table
Often called the Default-Free Zone (DFZ), this is the master list of all known IP prefixes and the best paths to reach them. It currently contains over 1 million unique IPv4 and IPv6 routes.
1. Announcing
The Origin AS 'announces' its IP space. Routers propagate this information so that every network knows the path back to the origin.
References
Advanced BGP Topics
Explore the complex protocols and architectural standards built on top of BGP's extensible framework.