IP in range checker
Put an address on the left and a block on the right. If it does not match, you get how far outside it falls — usually the fastest way to spot an off-by-one in a firewall rule. Put a block on the left instead to compare two blocks.
192.168.1.130 is inside 192.168.1.0/24
- Range
- 192.168.1.0 – 192.168.1.255
- Addresses in range
- 256
- Position
- 131 of 256
Blocks nest, ranges overlap
A CIDR block is a prefix plus a length, so the set of addresses it covers always starts on a power-of-two boundary and has a power-of-two size. That constraint is what makes routing tables searchable, and it also means two blocks can never half-overlap.
A first–last range has no such constraint. 10.0.0.5–10.0.0.20 is a perfectly good range and a terrible block — it takes several CIDR blocks to express. When a firewall accepts ranges and your documentation records blocks, this is where the mismatches come from.
The blocks worth memorising
Most "is this address internal?" questions are answered by this table rather than by a calculator.
| Block | Addresses | Meaning |
|---|---|---|
| 10.0.0.0/8 | 16,777,216 | Private (RFC 1918) |
| 172.16.0.0/12 | 1,048,576 | Private (RFC 1918) |
| 192.168.0.0/16 | 65,536 | Private (RFC 1918) |
| 100.64.0.0/10 | 4,194,304 | Carrier-grade NAT (RFC 6598) |
| 127.0.0.0/8 | 16,777,216 | Loopback |
| 169.254.0.0/16 | 65,536 | Link-local (APIPA) |
| 224.0.0.0/4 | 268,435,456 | Multicast |
| 0.0.0.0/0 | 4,294,967,296 | Every address — the default route |
Frequently asked
- Can two CIDR blocks partially overlap?
- No. CIDR blocks form a tree: any two are either disjoint or one wholly contains the other. If two blocks share even one address, the one with the shorter prefix contains every address of the longer. Arbitrary first–last ranges are different — those can half-overlap, which is one reason ranges are harder to reason about than blocks.
- Why does 10.0.0.5/24 not mean what I expect?
- A CIDR block is defined by its network address, so 10.0.0.5/24 describes the block 10.0.0.0/24 — the host bits are ignored. Most tools accept it and silently normalise, which is convenient until you paste it somewhere strict and get an error. Write the network address when you mean a block.
- Does a /31 contain usable addresses?
- Both of them. RFC 3021 permits /31 on point-to-point links, where there is no need to reserve a network and broadcast address, so both addresses are assignable. A /32 is a single host route. The usual 'subtract two' rule applies only to /30 and shorter.
- Is 0.0.0.0/0 a real block?
- Yes — it is every IPv4 address, which is why it is the default route and why it appears in firewall rules meaning 'anywhere'. A checker should say every address is inside it, and this one does.
Doing this for thousands of addresses?
These calculators run in your browser and never send us your input. When you need geolocation, ASN and network data for addresses in bulk, the API answers in one call — no key required to try it.
curl https://api.ipaddresstoday.com/api/v1/8.8.8.8Other free tools
- Subnet calculatorNetwork and broadcast address, subnet mask, wildcard mask, usable host range and host count for any IPv4 block.
- CIDR to IP rangeConvert a CIDR block to its first and last address, or collapse an arbitrary address range into the smallest set of CIDR blocks.
- IP address converterConvert an IPv4 address between dotted-quad, decimal, hexadecimal, binary and octal.
- IPv6 expand & compressExpand an IPv6 address to its full 39-character form, or compress it to the canonical RFC 5952 short form.
- IP range generatorList every address in a CIDR block or a first–last range, ready to paste into a firewall rule or a script.
- Random IP generatorGenerate random IPv4 addresses for test fixtures and load tests — optionally inside a given block, and publicly routable only.
- Subnet mask cheat sheetEvery IPv4 prefix from /32 to /0 with its subnet mask, wildcard mask, host count and block size — plus a mask to prefix converter.
- IPv4 to IPv6 converterSee an IPv4 address in every standard IPv6 form: IPv4-mapped, 6to4, NAT64 and the deprecated IPv4-compatible notation.
- Reverse DNS name generatorBuild the in-addr.arpa or ip6.arpa PTR name for any address, and list the reverse zones covering a whole block.
- IP list sorter & deduplicatorPaste a messy list of addresses from logs or a spreadsheet. Get them sorted numerically, deduplicated, with the junk separated out.
- Bulk IP lookupLook up country, city, ISP and ASN for a whole list of addresses at once, and export the result as CSV.