What Is My ISP? How to Check the ISP and ASN of an IP

In short: Your ISP is the network your connection reaches the internet through, and its autonomous system number (ASN) identifies that network in routing. What Is My IP shows both for your own connection. For any address, a registry query names the holder of the block and an IP-to-ASN lookup names the network announcing it. To check a proxy, compare that network with the carrier you ordered.

An ISP lookup answers one question about an IP address: which network is it on? Our free What Is My IP page answers it for your own connection. What follows explains what the provider name and the ASN in a lookup mean and gives three ways to check any address. It then covers why two lookups sometimes name different organisations, and how to compare an address you bought with the carrier named on the order. ProxyJam sells static residential (ISP) proxies, each on a named carrier’s network, so the last part is a check our own buyers run. Our editorial policy explains how articles like this are sourced and corrected.

What do ISP and ASN mean in a lookup?

Your ISP is the company whose network connects you to the internet. The rest of the internet knows that network as an autonomous system (AS), and its autonomous system number (ASN) is how routing refers to it. RFC 1930 defines an AS as “a connected group of one or more IP prefixes run by one or more network operators which has a SINGLE and CLEARLY DEFINED routing policy”.

Addresses and AS numbers come down the same chain, which RFC 7020 describes. IANA allocates pools of both to five regional internet registries, and each registry serves the networks in its region, directly or through local registries. The five are AFRINIC, APNIC, ARIN, LACNIC and RIPE NCC (IANA). A provider receives blocks of addresses and an ASN from its registry, then hands addresses out to its customers.

Networks tell each other which address ranges they can reach over BGP, the routing protocol between autonomous systems. The network that starts an announcement writes its own ASN into the route’s path, which RFC 4271 calls originating the route. So when a lookup shows a provider for an address, it reports one of two records: the registry entry for the block, which names the holder, or the routing data, which names the AS announcing the block. A name appears beside an ASN because every AS number has a registration record naming the organisation that runs it.

How do you check which ISP an IP address is on?

Pick the method by whose address it is and which record you need.

Your own connection: What Is My IP

Open What Is My IP in the browser you want to check. Its Internet provider and Network (ASN) rows show the network of the address the page received, as labelled by Cloudflare, which serves the page: the request’s AS number and the organisation Cloudflare lists for it (Cloudflare’s Request reference). Nothing on the card is saved. With a proxy or a VPN on, the rows show the server’s network, because that is the connection the page receives.

Any address: a registry query

The registry record says who holds the block an address is in. RDAP is the current protocol for reading it, a JSON service over HTTPS that ARIN describes as “a Whois alternative” (ARIN). Queries follow the paths RFC 9082 defines, ip/ for an IPv4 or IPv6 address and autnum/ for an AS number:

https://rdap.arin.net/registry/ip/203.0.113.7
https://rdap.arin.net/registry/autnum/64496

Both values are reserved for documentation, so put the address you are checking in their place. When we tried it on 26 October 2026, ARIN’s server answered a query for an address in RIPE NCC’s region by redirecting it to RIPE NCC’s RDAP server, so in our test one starting point covered both regions. The older whois protocol on TCP port 43 (RFC 3912) returns the same kind of record as text:

whois 203.0.113.7

If your system has no whois command, open the RDAP address in a browser or use RIPEstat, described in the next section.

Read three things in the answer: the range of the block, the organisation, and the type of record. In ARIN’s records a direct allocation came from the registry itself, and a reassignment or reallocation was passed on by a provider to a customer of its own.

Any address: an ASN lookup by IP

An IP-to-ASN lookup reads routing data and returns the AS that announces the address. Team Cymru’s free IP to ASN Mapping service maps an address to “its BGP prefix, origin ASN, and registry record”, from BGP feeds of more than 50 peers, refreshed every four hours:

whois -h whois.cymru.com " -v 203.0.113.7"

It returns one line with the AS number, the address, the BGP prefix, a country code, the registry, the allocation date and the AS name, in this shape (the values are documentation placeholders):

AS      | IP               | BGP Prefix          | CC | Registry | Allocated  | AS Name
64496   | 203.0.113.7      | 203.0.113.0/24      | US | arin     | 2020-01-01 | EXAMPLE-NET, US

RIPE NCC’s RIPEstat shows the same routing view in a browser. For an ASN lookup on its own, the registry’s autnum/ query returns the organisation behind the number. A downloadable database such as MaxMind’s GeoLite ASN carries two fields per range, the autonomous system number and “the organization associated with the registered autonomous system number”, and answers without sending the address anywhere.

How others rate the address

None of these lookups says whether an address is listed anywhere. Our IP Checker looks an address up in four published lists and asks three fraud-scoring services about it, then gives one verdict with each source’s reading beside it. The check opens in the ProxyJam app and runs there once you sign in or create an account. Looking the address up in the published lists alone is free; the full check uses a free check if you have one and is otherwise charged to your wallet balance.

Why do two lookups name different networks?

They read different records, copied at different times. The table Why two lookups name different organisations lists the common cases, and three of them explain most disagreements.

The holder and the announcing network are different organisations. A registry record names whoever holds the block, and a route names whoever announces it. They match when a provider announces its own addresses, and they part when a holder lets another network carry its block. The Resource Public Key Infrastructure gives that permission a signed form: a route origin authorisation (ROA) “provides a means of verifying that an IP address block holder has authorized a particular AS to originate routes” for the block (RFC 6483).

A provider passed the block on. ARIN calls it a reallocation when the provider’s customer will issue pieces of the block to customers of its own, and a reassignment when the block is for the customer’s own use (ARIN). The registry record for the address can then name the customer, while the route still leaves through the provider’s AS. RFC 1930 covers a related case. It advises a site connected to a single provider to place its prefixes in an AS of that provider, and not to create an AS of its own. A lookup can then show the provider’s ASN even where the registry names the site as the holder.

A copy is out of date. Every database is a copy made at some moment. Team Cymru refreshes its routing data every four hours, and a downloaded file is as current as the day it was built. When two answers disagree, run both again and compare them by ASN, since one network can appear under a brand in one tool and a legal name in another.

For a proxy address, the answer that describes how its traffic reaches the internet is the announcing network, and it is the network we mean when we name a carrier on an address. A site that reads another database may still show a different name for it.

How do you check an address you bought?

By the network that announces it. Every ProxyJam ISP address is sold with a named carrier, and that name is the network that announces the address. The holder in the registry record can be another organisation, which is ordinary on a reassigned or leased block. The steps in Compare an address with the carrier you ordered take you from the order to both lookups; keep their outputs, since support needs them to look into a difference.

A match between the announcing network and the carrier you ordered is the result to expect, whatever name the registry record carries. If it is another network, write to support@proxyjam.com or the Telegram support bot listed on our FAQ, with the address, the order number, both outputs and the UTC time you ran them. Our terms set out these related rights:

• Free replacement. Section 2.5 of the Terms of Service names three grounds: the address stops responding, its geolocation moves outside the country you bought, or the target you identified at purchase refuses it. Free replacements are limited to 20 % of the addresses in an order per calendar month.
• The first order. Under section 2 of the Refund Policy, you can request a refund within 24 hours of your first order, for up to ten addresses, once per customer, and using the proxies in that window does not void the request.

A network lookup shows where an address is announced today. It cannot show how the address was used before you held it. For how others rate it now, run the IP Checker.

When does a lookup not answer the question?

• Where a device is. A lookup names a network. A location is a geolocation database’s estimate for the whole range, a separate dataset; what sites read to place a visitor is covered in viewing your website from another country.
• Who used an address. Which subscriber held an address at a given time is known to the provider, which does not publish it.
• Whether a site will accept an address. Each site applies its own rules. The IP Checker reports what published lists and scoring services say, and only a request to the site itself settles the rest.
• An address on a mobile network. We do not sell mobile addresses yet. The mobile proxies page explains how they work.

In the United States, the US ISP proxies page lists the 19 named carriers our addresses are on, so you can look a carrier’s network up before you order. The same product is described under its other name on static residential proxies. The definition of an ISP proxy explains why a network lookup returns a provider for an address served from a data centre, and residential vs datacenter proxies compares what the registry shows for each type. The catalogue covers 77 countries on the ISP proxies page, priced per IP per period on the pricing page.