An ASN (autonomous system number) is a unique number assigned to a network that controls its own routing policy on the internet, such as an ISP, cloud provider or large company. Apple is AS714, Cloudflare AS13335, Google AS15169. Networks use their ASN when announcing their IP ranges with BGP.
How it works
Autonomous systems
The internet is a network of about 75,000 independently run networks, each called an autonomous system (AS). Each has a number, assigned by a regional internet registry: ARIN (North America), RIPE NCC (Europe, Middle East), APNIC (Asia-Pacific), LACNIC and AFRINIC.
ASNs were 16-bit numbers (up to 65,535); since 2007 they can be 32-bit, so you'll see large ones like AS395747. Ranges 64512–65534 and 4200000000–4294967294 are private, for internal use.
What an ASN tells you
Looking up the ASN of an IP address tells you which network operates it: whether a connection goes to Apple, Amazon Web Services, Cloudflare or a residential ISP. That's often more useful than the IP's location, especially for CDNs and cloud servers.
ASNs and BGP
Each AS announces its IP prefixes to its neighbours using BGP, along with the path of ASNs the route has crossed. That's how traffic finds its way between networks.
Examples
| ASN | Network |
|---|---|
| AS714 | Apple |
| AS13335 | Cloudflare |
| AS15169 | |
| AS16509 | Amazon (AWS) |
| AS8075 | Microsoft |
| AS7922 | Comcast |
$ whois -h whois.cymru.com " -v 17.253.144.10"
AS | IP | BGP Prefix | CC | Registry | Allocated | AS Name
714 | 17.253.144.10 | 17.253.144.0/24 | US | arin | 1990-04-16 | APPLE-ENGINEERING - Apple Inc., US
Apple holds all of 17.0.0.0/8 but announces smaller pieces of it, like this /24, from different places.
On a Mac
whois -h whois.cymru.com " -v <IP>" returns the ASN and network name for any IP address. whois AS714 shows the registration record for an ASN.
See it in the app
LightAtom's Map groups destinations by country and city; look up an address's network with whois -h whois.cymru.com " -v <IP>".
Frequently asked questions
What does ASN stand for?
Autonomous system number: the identifier of a network that manages its own routing on the internet.
How do I find the ASN of an IP address?
Run whois -h whois.cymru.com " -v
Do I have my own ASN?
No. Home users use their ISP's ASN. Organisations need their own only if they connect to several providers or run their own IP space.
What is Apple's ASN?
AS714 is Apple's main ASN; Apple also uses others, like AS6185.