Quick lookup: Need to find the ASN for an IP? Use the MyIPNow WHOIS Lookup.
What is an Autonomous System (ASN)?
An Autonomous System (AS) is basically a bunch of IP networks that one organization controls and manages together. They all follow the same routing rules and policies. Each AS gets assigned its own unique number, called an Autonomous System Number (ASN).
Key ASN concepts
Download CSV| Term | Description | Why it matters | Example |
|---|---|---|---|
| ASN | The unique ID for an autonomous system | How it's identified for routing | AS13335 |
| IP Prefixes | The IP ranges that an ASN announces | Shows who owns which traffic | 104.16.0.0/12 |
| BGP | The protocol that handles routing between ASNs | Decides how traffic gets routed | AS_PATH |
| Upstream | Your provider's ASN | Gets you connected to the internet | Tier-1 ISP |
| Downstream | Your customer's ASN | Where traffic originally comes from | Hosting provider |
| Peering | Direct connection between two ASNs | Traffic goes straight between them | IXP peering |
| RIR | The organization that gives out ASNs | Controls who gets what | ARIN / RIPE |
| AS-SET | A collection of multiple ASNs | Used for setting routing policies | IRR objects |
How ASNs are used
- Moving traffic around the internet
- Figuring out who owns which IPs and who's responsible
- Setting up security rules and routing policies
ASN vs IP address vs ISP
- An IP address is what identifies a specific device.
- An ASN identifies the network that's announcing those IP ranges.
- An ISP is the actual company running things-they might operate one or more ASNs.