IP Address Range Check

What this tool does

The IP address range check tells you whether the IP address you are connecting from (or one you type in) falls inside an IP address range written in CIDR notation or a similar format. It supports both IPv4 and IPv6, and every check runs inside your browser. You can keep up to 10 ranges on your device; the next time you open this page, all of them are re-checked automatically against your IP at that moment, so confirming things after switching networks or connecting to a VPN takes only seconds.

The reasoning is shown bit by bit. A 32-bit (IPv4) or 128-bit (IPv6) diagram and a side-by-side comparison of the fully expanded addresses show how far the leading bits of your IP agree with the network portion of the range and where they diverge. You also get the first and last address of the range, the address count, the subnet mask, the number of /48s and /64s for IPv6, the minimal CIDR blocks that cover a start-end span, and an estimate of the allocation holder from GeoLite2.

When to use it

• After connecting to your company VPN, to confirm that your traffic really leaves through the IP address range registered in the office allow list.
• Before and after editing a cloud security group or firewall rule (AWS and others), to verify that the CIDR block you registered actually includes the IP you are using right now.
• Before writing an IP address range into a server or application allow list, to check that the format is correct and that it covers exactly the addresses you intend.
• To read off the IPv6 prefix (/64 or /56) your provider has delegated to your home and see whether it has changed over time.

How to read the results

• "In range" means the leading bits of the checked IP match the network portion of the range exactly. The IP is most likely connecting from within the range allocated to that organization or connection.
• An "Out of range" row shows how many leading bits match and at which bit the addresses diverge. A larger matching count means a closer range, but a single differing bit is enough to be outside it.
• In the bit diagram, ink-filled cells are bits that match the network portion of the range, red cells are mismatching bits, and outlined cells are the host portion (bits that are not compared). The first differing bit has a thicker outline.
• An IPv4 address and an IPv6 range (or the other way round) cannot be compared, so the row shows "Cannot compare". Only the IP you used to reach this page is checked.
• The allocation holder is an estimate obtained by looking up the first address of the range in the GeoLite2 database. Private and reserved addresses have no holder and none is shown.

Frequently asked questions

How many IP addresses are in a /32 or /128 range?

Both /32 (IPv4) and /128 (IPv6) designate exactly one address. Each time the prefix length gets 1 shorter, the address count doubles: an IPv4 /24 holds 256 addresses and a /16 holds 65,536. If you enter a single IP address, this tool treats it as /32 or /128.

How many addresses are in an IPv6 range like 2001:268::/32, and how does it relate to /64?

An IPv6 /32 contains 2^96 addresses (about 7.9 × 10^28). Split into /64s, the size used for a single LAN, it holds 2^32 of them (about 4.3 billion). Providers hold large ranges such as a /32 and delegate a /64 or /56 out of it to each customer.

What does "In range" actually tell me?

That you are connecting from within the range held by that organization or connection. For example, if your IP is in the range of your company VPN's exit, your traffic is leaving through the VPN; if it is in a CIDR block you registered in a cloud security group, that rule will admit your connection.

Are the ranges I enter stored on the server?

No. Ranges are stored only inside this browser on your device (localStorage) and are not sent to the server, and the checks themselves also run in the browser. The tool does query the location API with the first address of a range to show the allocation holder, and it looks up your own IP to know what to check. Manually entered IPs are never stored.

Can I check IPv4 and IPv6 at the same time?

The IP that is checked is the one you used to reach this page, which is either IPv4 or IPv6. To check the other one, enter that address under "Check a different IP". Changing the connection side, such as disabling IPv6 in your browser or OS settings, changes which IP is used to reach the page.