ASN Lookup
Who runs an autonomous system, and every prefix it announces — ready for a firewall.
Try before you buy.
- Free preview: the AS, every count and the registration, with the first prefixes of the list (up to 10) and the first lines of each firewall export.
- Locked until you unlock it: download and copy.
- Unlock: Pro pass, ₹179 for 30 days or ₹79 for 1 week, a one-time payment that never renews. Unlock: Pro pass, $5.99 for 30 days or $2.99 for 1 week, a one-time payment that never renews.
Ways to unlock shows how to get the full result.
Printing this result is locked in the free preview.
Look up an autonomous system
Networks with that name
| AS number | Name | Country | IPv4 ranges | IPv6 ranges |
|---|
Address
Autonomous system
Registration (RDAP)
Asking the registry…
Prefixes this AS originates
Loading the routing data…
| Prefix | First address | Last address | Addresses |
|---|
Export for a firewall or cloud
Prefixes and AS names come from a snapshot of the IPtoASN data (PDDL) built into this page; the registration is asked live from the registry. Look up one IP address in depth. Look up thousands of addresses at once. Merge or subtract prefix lists.
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About the ASN Lookup
An autonomous system (AS) is a network that takes part in internet routing under its own number — an internet provider, a cloud, a CDN, a university or a large company. Enter an AS number (AS13335, 15169, or asdot 1.10), part of an AS name (“hetzner”), or an IP address to find the network that routes it, and see who holds the AS and what it announces.
The registration comes live from the regional internet registry over RDAP: the holder, registry, country, registration and last-changed dates and the abuse contact. The prefixes come from the IPtoASN routing snapshot built into this page: every IPv4 and IPv6 block the AS is the origin of, merged into the fewest CIDR prefixes, with address counts. With a pass, export them as a plain list, CSV, nginx allow or deny rules, iptables/ip6tables rules, ipset sets or AWS security group JSON.
Without a pass the result is a free preview: every count and the registration, with the first prefixes of the list and the first lines of each firewall export. The full lists, copying and the downloads unlock with a Pro pass.
How to use it
- Type an AS number such as
AS13335, part of a network’s name such ascloudflare, or an IP address such as8.8.8.8, and press Look up. - For a name, choose the network from the list of matches (largest networks first).
- Read the summary: the AS name and country, how many IPv4 and IPv6 prefixes it originates and how much address space that is, and the registration with the abuse contact.
- Browse the prefixes, show only IPv4 or IPv6, or filter them by typing part of an address.
- Under Export for a firewall or cloud, choose the format and options, then Copy or Download the rules — with a pass, or after unlocking this result.
Examples
AS13335
AS13335 — CLOUDFLARENET · United States · registry ARIN · over a thousand IPv4 and over a thousand IPv6 prefixes, among them 1.0.0.0/24 and 1.1.1.0/24
8.8.8.8
8.8.8.8 is in 8.8.8.0 – 8.8.8.255, originated by AS15169 (GOOGLE)
AS64500, export “nginx allow / deny rules”, rule “Block these prefixes”
# AS64500 …: 2 prefixes (IPtoASN snapshot) deny 192.0.2.0/24; deny 2001:db8::/32;
AS64500 and these prefixes are documentation values; a real AS gives its real prefixes.
AS64512
Private-use AS number (RFC 6996): anyone may use it inside their own network, so it identifies no one on the internet
Common uses
- Finding out which company is behind an attack, a scraper or spam in your logs, and where to report it.
- Blocking (or allowing) a whole hosting provider or cloud in nginx, iptables or an AWS security group.
- Checking which prefixes your own network or a customer announces before setting up filters or peering.
- Turning an AS name you saw in a traceroute or an e-mail header into its number, registry and contacts.
Where each answer comes from
- Registration: IANA’s RDAP bootstrap file for AS numbers names the regional internet registry — ARIN, RIPE NCC, APNIC, LACNIC or AFRINIC — and your browser asks it for the AS’s autnum record (RFC 9083 §5.5). LACNIC hands Brazilian AS numbers on to NIC.br.
- Prefixes and AS names: a snapshot of IPtoASN, released into the public domain under the PDDL, built from public BGP routing tables. For each block of addresses it records the origin AS of the most specific route that covers it. Neighbouring blocks of the same AS are merged and split into the fewest CIDR prefixes (RFC 4632).
- Special numbers: IANA’s Special-Purpose AS Numbers registry: AS 0 (RFC 7607), AS_TRANS 23456 (RFC 6793), documentation (RFC 5398), private use (RFC 6996) and the reserved last numbers (RFC 7300).
Prefixes an AS “originates”
A route on the internet is announced by the network that holds the addresses — the origin AS — and passed on by the networks between. This page lists the address space for which the AS is the origin of the most specific route. Two things follow. A large block with a hole in it shows up as the block minus the hole, when another network announces the hole more specifically. And address space the AS holds but does not announce, or announces only through another network, is not listed: the registration and the routing table are different questions. Routing changes every day, so the newest changes may be missing from the snapshot.
AS numbers: 16-bit, 32-bit and asdot
AS numbers were 16-bit (1 to 65,535) until 4-byte AS numbers (RFC 6793) raised the limit to 4,294,967,295. They are written as plain decimal numbers (RFC 5396, “asplain”); some router configurations use asdot, the high and low 16 bits joined by a dot, so 1.10 is AS65546. Older routers that understand only 2-byte numbers see AS_TRANS (23456) in place of a 4-byte number.
Using the exports
- nginx: “Allow only these prefixes” adds a final
deny all;; put the lines in a server or location block. - iptables: one rule per prefix with a comment naming the AS; IPv6 prefixes get
ip6tablesrules. For long lists use ipset: one set per IP version and one rule that matches the set. - AWS: the JSON is the
--ip-permissionsvalue ofaws ec2 authorize-security-group-ingress. A security group holds 60 inbound IPv4 and 60 inbound IPv6 rules by default. The quota can be raised, but rules per group times security groups per network interface cannot exceed 1,000, and a prefix list referenced in a rule counts as its maximum number of entries (Amazon VPC quotas), so a network with hundreds of prefixes is better filtered on the server with nginx, iptables or ipset.
Blocking a whole AS also blocks everyone else on it: a cloud or hosting AS carries thousands of customers, and a CDN AS carries the websites behind it.
Limitations
- The prefixes are a snapshot of the routing table: networks that started or stopped announcing a prefix since then are not reflected, and prefixes announced only as more-specifics of another network’s block may be split.
- The routing data comes from public BGP collectors; routes seen only between private peers do not appear.
- Registries limit how many RDAP requests they answer; some corporate networks and content blockers stop requests to them.
- AS names are the short names in the routing data (such as GOOGLE or AMAZON-02); the holder in the registration is the organisation’s registered name.
Privacy
Sends data to online services
Your browser asks IANA’s bootstrap file and the regional internet registry (RDAP) for the AS number’s registration. The prefixes and AS names come from IPtoASN data files on MySmartCoPilot itself; an IP address you enter is looked up in those files and is not sent anywhere.
Frequently asked questions
What do I get without a pass?
Without a pass, ASN Lookup shows the AS, every count and the registration, with the first prefixes of the list (up to 10) and the first lines of each firewall export. Until you unlock it, the result can’t be downloaded or copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
How do I find the ASN of an IP address?
Type the address. The page finds the range it falls in and the AS that originates that range in the routing snapshot, then shows that AS. For the owner, abuse contact and location of the single address, use the IP Address Lookup.
Can I block a whole company with its ASN?
Yes: with a pass, export its prefixes for nginx, iptables, ipset or an AWS security group. Remember that a cloud, hosting or CDN AS is shared by many customers, so the block may hit people and sites you did not mean to block. Companies with several networks have several AS numbers — search by name to find them.
Why are there fewer prefixes than other sites show?
Sites that list announced routes count every announcement, including overlapping ones (a /16 and the /24s inside it). This page merges overlapping and neighbouring blocks of the AS into the fewest CIDR prefixes, so the list is shorter for the same addresses. Space inside its blocks that another network announces more specifically is left out, because that network is the origin there.
What is a private AS number?
AS 64512–65534 and 4200000000–4294967294 are reserved for private use (RFC 6996), like private IP addresses: anyone may use them inside their own network, so they belong to no one on the internet and have no registration. If one shows up as the origin of a public route, a private network’s routes have leaked.
Who do I report abuse from an AS to?
To the abuse contact in the registration. For a single address, the Abuse Contact Lookup finds the contact of the exact network block, which is often a customer or a smaller provider rather than the AS itself.