What is Border Gateway Protocol and BGP announcements?

Border Gateway Protocol (BGP) is the routing protocol that governs how traffic moves between autonomous systems on the internet. It is the mechanism by which the global routing table is built and maintained — every AS uses BGP to tell its neighbours which IP address prefixes it can deliver traffic to.

How BGP announcements work

When an AS wants to make its IP address space reachable to the rest of the internet, it sends a BGP update message to its neighbouring ASes. This message — called a BGP announcement — contains the IP prefix being advertised, the AS path (the sequence of ASes traffic will traverse to reach it), and other routing attributes.

Neighbouring ASes receive the announcement, add the prefix to their routing tables, and propagate the announcement onwards. This process continues until the prefix has been distributed throughout the global routing table, making the AS's address space reachable from anywhere on the internet.

Why BGP matters for IP geolocation and network analysis

BGP data is one of the primary inputs for IP geolocation. By analysing which AS is announcing a given IP prefix and understanding the geographic footprint of that AS's infrastructure, it is possible to make informed estimates about where an IP address is in use.

BGP announcements are also essential for detecting network anomalies such as route leaks and prefix hijacks — situations where traffic is being directed through unintended ASes. BigDataCloud's BGP Active Prefixes API provides a current view of all actively announced prefixes on the global routing table.