IP to ASN Lookup Tool
Every IP address on the internet belongs to an autonomous system. Enter any IPv4 or IPv6 address to find out which organization owns it. Our tool shows you the ASN number, network prefixes they control, and registration details by checking real time data. Perfect for network troubleshooting, security analysis, identifying email sources, or understanding who's behind any IP address.
What is an Autonomous System?
The internet isn't one giant network. It actually consists of many smaller networks that are connected to one another. These smaller networks get the name autonomous system, also can be called AS.
Think of an AS like a neighborhood in a city. Each neighborhood has its own streets and management. Similarly, each AS has its own IP addresses and routers managed by one organization. Your internet service provider runs an AS. Amazon runs one for AWS. Google has one. Universities and big companies have them too.
The word "autonomous" means independent. The organization running an AS controls how it operates. They decide routing policies, which networks to connect with, and how traffic flows through their infrastructure.
What is an ASN?
Every AS needs a unique identification number which is called is the autonomous system number or ASN for short.
Regional internet registries assign these numbers to make sure no duplicates exist. The five registries are ARIN (North America), RIPE (Europe/Middle East), APNIC (Asia Pacific), LACNIC (Latin America), and AFRINIC (Africa).
ASNs are written with "AS" in front, like AS15169 for Google or AS7922 for Comcast. The original format was 16-bit (numbers 1 to 65,535). As the internet grew, 32-bit ASNs were introduced, extending the range to over 4 billion possible numbers.
How IP Addresses Connect to ASNs
Every IP address belongs to an ASN. When an organization gets an ASN, they also receive IP address blocks called prefixes.
A prefix like 203.0.113.0/24 contains 256 individual IP addresses. The organization decides how to use them for their own infrastructure, customer assignments, or future expansion.
Large networks manage hundreds of prefixes. They accumulate these blocks over time through new allocations, acquisitions, or geographic expansion.
When you look up an IP address with our tool, we check BGP routing tables to find which ASN announces that IP. This tells you who owns and controls that address. It's like reverse phone lookup, but for internet infrastructure.
FAQs
What's the difference between IP to ASN lookup and ASN lookup?
IP to ASN lookup is performed by beginning with one IP Address which gives you the ASN holding it. But an ASN lookup will start with an AS number and you will receive all the IP ranges under the control of that autonomous system along with all the network details. In case you are aware of the ASN, then use our ASN lookup tool instead.
What's the difference between IPv4 and IPv6 prefixes?
IPv4 is the original format of internet addresses, for example 192.0.2.0. IPv4 address works with 32 bits, so it makes around 4.3 billion possible numbers. This was a lot in the early days, in the 1980s. However, a problem appeared when there were a lot of new machines and devices like computers, mobile phones, the internet of things, and servers. It turned out that we did not have enough addresses for all.
So, IPv6 was created for solving this issue. Instead of 32 bits, IPv6 addresses use 128 bits, written like 2001:0db8:85a3::8a2e:0370:7334. It is said to be possible to have 340 undecillion addresses. This is big enough for each tiny sand piece on the planet to get its own IP.
Nowadays, both IPv4 and IPv6 are working for the internet. When you see counts for prefix blocks in ASN information, you are seeing the number of blocks managed for each kind.
A prefix means a group of IP numbers. IPv4 prefix such as 192.0.2.0/24 is actually 256 IPs, while an IPv6 prefix like 2001:db8::/32 gives 79 octillion addresses. When you see the prefix number, it tells the amount of ranges announced through BGP by the group.
Why does my search show "bogon IP address"?
Bogon IPs are the ranges, which are not a part of the public internet space. This consists of private addresses (192.168.x.x, 10.x.x.x) and localhost (127.0.0.1), as well as block of the reserved addresses and block of the unallocated addresses. No ASN assignments are in these addresses since they are not globally routable.
Can I look up multiple IPs at once?
The tool is to be used in single IP lookups. In case you require checking several IP addresses or you want to automate lookups, we have options of bulk processing in our API section above.