ASN lookup
ASN lookup: enter an IP address or an AS number such as AS15169 to see the network operator and the prefixes it announces.
Data comes from RIPEstat and is requested when you press the button.
About the asn lookup
ASN lookup: enter an IP address or an AS number such as AS15169 to see the network operator and the prefixes it announces.
Part of SmartCalcy’s data & networking tools. It runs in your browser with no account, uses your own currency and units (change them at the top of the page), and gives estimates for information only, so check official guidance before you rely on a result.
How to use the asn lookup
What it calculates and when to use it
Finds the autonomous system number (ASN) of the network that announces an IP address, or the holder and announced address ranges of an AS number you already know. An ASN identifies one network on the internet, such as a provider, a cloud company or a university.
How to use it, step by step
- Enter an IP address, or an AS number such as AS15169.
- Press “Look up ASN”.
- Read the AS number, holder and whether it is visible in global routing.
- Check the list of announced prefixes underneath.
What each input means
- IP address or AS number – An IPv4 or IPv6 address, or an AS number with or without the “AS” prefix.
How to read the results
- AS number and holder – The network’s number and the organisation that holds it.
- Announced – Whether the network is currently visible in the global routing table.
- Prefixes announced – The count of IPv4 and IPv6 address ranges the network advertises, with a sample of them.
The formula
No calculation. Networks use the BGP protocol to announce which address ranges (prefixes) they can reach, each under an AS number. RIPEstat reads these announcements from routing collectors around the world.
A worked example
Looking up 8.8.8.8 returns AS15169, held by Google LLC, which announces 8.8.8.0/24 among many other ranges.
Assumptions and limits
- Data comes from RIPEstat and is requested when you press the button.
- Only the first part of a long prefix list is shown.
- An address that nobody announces cannot be mapped to a network.
Common mistakes
- Entering an AS number with a typo or extra text, such as “AS 15169 Google”.
- Assuming one organisation has one ASN. Large companies often operate several.
- Reading the ASN as a location. It identifies a network, which can span many countries.
Frequently asked questions
What is an ASN?
An autonomous system number is a unique number given to a network that has its own routing policy on the internet.
What is a prefix?
A range of IP addresses written in CIDR form, such as 8.8.8.0/24, that a network announces to the rest of the internet.
Why does an address have no ASN?
The address may be private, unallocated or not currently announced by any network.
Is this the same as IP WHOIS?
No. WHOIS shows the registry record. ASN lookup shows which network actually announces the address in routing.