Bulk IP to ASN lookup: which network owns each IP or domain?
In short: Paste IP addresses or domains and get each one's autonomous system number (ASN), the network's registered name, the routed prefix and the registry, from Team Cymru's public routing data. Limit: The ASN names the network that announces the IP, which may be a CDN or cloud provider rather than the company using the server.
A bulk IP to ASN lookup tells you which network announces each IP address: its autonomous system number (ASN), the network's registered name, the routed prefix and the regional registry. Paste up to 100 IPs or domains, or 500 after a free Google sign-in; a domain is resolved to its IP address first. Results come from Team Cymru's public IP-to-ASN data over DNS. CSV out.
Price: this tool is free. Checking a whole email list is from $9/mo, and the first 100 checks are free with Google, no card. Check your list free nowSee pricing
Sample result
8.8.8.8 is announced by AS15169 (GOOGLE), prefix 8.8.8.0/24, registered with ARIN.
- IP
- 8.8.8.8
- Network
- Prefix
- 8.8.8.0/24
What this means for you
The ASN names the network an IP or website runs on: a cloud, a CDN, an ISP or a hosting company.
- Origin ASN and network name
- Routed prefix and registry
- Domains resolved to an IP first
- Group by network, CSV out
- ASN
- BGP
- Hosting
By SimpleVerifier Team · Last updated
Also in: Português (Brasil) · Español · Deutsch · Français · Türkçe · 简体中文 · Русский · Nederlands · Italiano · Tiếng Việt · Bahasa Indonesia · Polski · العربية · Українська · Čeština · Magyar · 日本語 · 한국어
Looked up the networks behind a lead list's domains?
- The network a website runs on says nothing about whether the email addresses at that company work. Upload the list at /verify for a mailbox check on each address.
- The first 100 email checks are free with a Google sign-in, no card. For each domain's mail provider rather than its web host, use the bulk email provider lookup.
How do I find the ASN of many IP addresses at once?
- Paste IP addresses or domains, one per line, up to 100 a run, or 500 after a free Google sign-in. A domain or website URL is resolved to its first IPv4 address (IPv6 when it has none).
- Press Look up networks. Each IP gets one DNS query for its origin ASN and prefix, and each new ASN one more for its name, 25 items a request.
- Read each row: the IP, the ASN, the network name (for example GOOGLE or AMAZON-02), the routed prefix, the registry and the country the registry lists for the network.
- Filter by network to see how many of your IPs or domains sit on the same provider, and download the CSV.
Example
- You enter
- Two IPs and a domain:
8.8.8.8,1.1.1.1andacme.example. - You get
- 8.8.8.8: AS15169, GOOGLE - Google LLC, prefix 8.8.8.0/24, ARIN. 1.1.1.1: AS13335, CLOUDFLARENET - Cloudflare, Inc., prefix 1.1.1.0/24, APNIC. acme.example is resolved to its IPv4 address first, then shown with the network that announces it. Download the CSV.
- Limits
- Up to 100 a run without an account and 500 when signed in with Google, counted over a minute. 25 items a request; DNS queries to Team Cymru's IP to ASN service only.
What is an ASN?
An autonomous system is a network run under one routing policy, such as a cloud provider, an ISP or a large company, and its autonomous system number (ASN) identifies it on the internet. Each one announces the blocks of IP addresses it routes. RFC 1930 describes the idea; regional registries such as ARIN, RIPE NCC and APNIC assign the numbers.
So the ASN of an IP tells you whose network it is on: 8.8.8.8 is announced by AS15169 (Google), and an address in AWS shows an Amazon ASN. That is often the quickest way to tell which hosting company or ISP sits behind an IP or a website.
Where does the data come from?
From Team Cymru's IP to ASN mapping service, which publishes the origin ASN and prefix of every routed IP from global routing (BGP) data, and each ASN's registered name, as DNS TXT records. This tool sends two DNS queries for each new IP or ASN and nothing to the IPs themselves.
The country column is the country the regional registry lists for the network, not where the server physically is. A US-registered cloud provider shows US for servers in Frankfurt or Singapore. Use it as the network's home, never as a location.
Why would a cold emailer look up ASNs?
To read a lead list at the network level. Many domains on the same small hosting network can mean a batch of placeholder or reseller sites, and a company whose website and mail both sit on a big cloud provider is set up differently from one on a home broadband line. For your own sending, the ASN of an IP in a bounce or a blocklist notice tells you which provider to talk to.
Pair it with the bulk reverse DNS lookup for each IP's hostname, and the website host checker to name the platform (Shopify, Vercel, Wix) behind a site rather than just its network.
Why do some IPs show no ASN?
An IP that no network currently announces has no origin ASN: unused space, a range being moved between providers, or a private or reserved address, which this tool skips. A domain without an A or AAAA record has no IP to look up.
Some prefixes are announced by more than one network at once; the row then lists every ASN Team Cymru returns. When the name lookup fails, the ASN is still shown, without a name.
How is this different from a WHOIS lookup on each IP?
| This tool | IP WHOIS | |
|---|---|---|
| Items per run | 100, or 500 signed in | One at a time |
| What it shows | The network that routes the IP now | Who the block is registered to |
| Accepts domains | Yes, resolved to an IP | No |
| CSV export | Yes | Copy and paste |
Who uses this tool, and for what?
- Cold emailers
- See which hosting networks a lead list's domains sit on, and spot clusters of sites on the same small network.
- Deliverability consultants
- Name the provider behind the IPs in bounce messages, headers or blocklist notices.
- Security teams
- Group IPs from a log by the network that announces them.
- Agencies
- Check which cloud or hosting provider each client website runs on before a migration.
What can’t this tool tell you?
- The ASN names the network that announces the IP, which may be a CDN or cloud provider rather than the company using the server.
- The country is the network's registry country, not the server's location.
- A domain is resolved to one IP; sites with many IPs or a CDN may show a different network from other visitors' answers.
- Data comes from Team Cymru's service and can lag a routing change by a few hours.
- Up to 100 IPs or domains a run without an account, 500 signed in.
Common questions
- How do I find the ASN of an IP address?
- Paste it into an IP to ASN lookup like this one. It returns the ASN that announces the IP, the network's name, the routed prefix and the registry. You can paste up to 100 at once, or 500 signed in.
- Can I look up the ASN of a domain?
- Yes. Paste the domain and it is resolved to its first IPv4 address (or IPv6 when it has none), and that IP's network is shown. A website behind a CDN shows the CDN's network.
- Is this IP to ASN lookup free?
- Yes. Up to 100 IPs or domains a run without an account, and up to 500 a run when you sign in with Google, with no card.
- Does the country show where the server is?
- No. It is the country the regional registry lists for the network that owns the IP. Cloud providers register in one country and run servers in many.
- Where does the ASN data come from?
- From Team Cymru's public IP to ASN mapping, which is built from global routing data and served over DNS. Nothing is sent to the IPs being looked up.
- Can I find the hosting provider of many websites?
- At the network level, yes: paste the domains and the ASN name shows the network, such as AMAZON-02 or CLOUDFLARENET. For the platform behind each site, use the website host checker.
Sources
A tidy list can still be full of dead addresses.
Extracting, deduplicating and syntax checks all work on the text of an address. None of them can tell whether the mailbox exists. Only the server that hosts it can answer that, through an SMTP check, and that is what the paid product does.
- Upload the cleaned file as it is: CSVs up to 100,000 rows
- A real SMTP mailbox check on every row, with catch-all detection
- Small list? Starter at $9/mo covers 2,500 emails a month, cancel anytime
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.