AS Path Finder
How does the Internet reach a network? Enter an IP address, a prefix or an AS to see who carries traffic to it and who carries it to them. Add your own AS to see the path you most likely take.
Find a path
Where to, and from where
API
Use it from a script
The same answer is JSON at https://api.notoolkit.com/v1/as-path/{address, prefix or asn}?from={asn}: the ingress as a tree and the likely route, hop by hop. Try it and read every field on its demo page.
How it works
Common Questions
How is the path worked out?
From the paths real routers chose. RouteViews and RIPE RIS collect full BGP tables from hundreds of networks, and every path in them shows which AS each network forwards to next. For the prefix you ask about, the tool reads every AS within four hops of the origin and the next hop it takes. That is the drawing. If your AS is on one of those paths, its route is shown as it was seen.
What does "inferred" mean?
Nobody collects a full table from most networks, so their routes have to be guessed. The tool climbs from your AS through its upstream providers, using AS relationships inferred from the same data, and follows the rule most networks route by: a route from a customer is preferred to one from a peer, and that to one from a provider, then the shorter path. Where it meets an AS whose route was seen, it follows that one. The inferred hops are drawn dashed.
Why is an IP address better than an AS?
Networks often announce different prefixes to different upstreams, for traffic engineering or because a prefix belongs to a customer. With an address, only the prefix that covers it is read, so the drawing shows how that address is actually reached. With an AS, all of its prefixes are read together.
How current is it?
The RouteViews tables are read every 4 hours and RIPE RIS every 8. For an address or prefix, the paths our own looking glass collectors hold are added live.
Is this the path my traffic will take?
It is a best guess at the AS-level path, not a traceroute. Networks can prefer one route over another for reasons no public data shows, and return traffic usually takes a different path. A seen route is far more reliable than an inferred one.