BGP guides

Short guides to public routing data, written for people who look at BGP routes as part of their job and for anyone learning to read them. Each one uses real maps from this site.

If you are new to this, start with how to read a BGP map. It explains what the boxes, arrows and numbers on a map stand for, using the live map of 1.1.1.0/24, and everything after it assumes you know that much. What is an AS path? goes one level down, into the list of networks a route carries: which way it is written, how routers use it, and what prepending does to it.

The other three answer questions that come up when something breaks. Which network announces an IP address? gets you from an address to the prefix and the origin AS, and shows where that answer and whois stop agreeing. Finding upstream providers reads transit relationships out of the paths and says how far the shares can be trusted. Tier 1 networks lists the networks that buy no transit at all, each linked to its own map.

Three newer guides go one level deeper. Origin, upstream and peer explains the roles the networks on a path play and why peers rarely show up in route data. BGP map, looking glass or traceroute says which of the three answers which question. How to spot a BGP hijack on a map lists the signs in route data and the harmless look-alikes that fool people.

Two guides added in October cover practical questions. Is my prefix visible on the Internet? goes through what a map says about an announcement and the usual reasons one is missing or only partly seen. BGP visualizers and map tools compared separates path maps, replays, AS explorers and looking glasses by the question each one answers.

All guides

• How to read a BGP mapWhat the boxes, arrows, numbers and colours on a map mean.
• How to find the upstream providers of a networkReading transit providers from AS paths, and what the shares mean.
• Which network announces an IP address?From an address to its prefix and origin AS, and when whois disagrees.
• What is an AS path?How the AS path is written and used, and what prepending does.
• Tier 1 networksThe transit-free networks, with a link to each one's map.
• Origin, upstream and peer: who is who on a BGP mapThe roles networks play on a path, and why peers hide.
• BGP map, looking glass or traceroute: which one to useWhich tool answers which routing question.
• How to spot a BGP hijack on a mapThe signs of a hijack in route data, and the harmless look-alikes.
• Is my prefix visible on the Internet?Reading visibility from a map and the common reasons a prefix is missing.
• BGP visualizers and map tools comparedPath maps, replays, AS explorers and looking glasses, and when to use each.

Where the data comes from

Every map and every number in the guides comes from RIPE RIS, the RIPE NCC's network of route collectors, read through the RIPEstat API. A collector peers with hundreds of networks around the world and records the routes each of them sends, so a map shows how the prefix looks from all of those places at once rather than from a single router. The About page covers how often maps refresh and how route changes are noticed. If you came here from BGPView, this page lists which of its lookups work here.