Why did 10.0.0.5/24 convert to 10.0.0.0/24?

10.0.0.5 has host bits set: bits past the prefix length that aren't zero. A block always starts at its network address, so the converter masks those bits off and says so on that row rather than refusing the entry.

What is a wildcard mask?

The netmask inverted: a /22 has the netmask 255.255.252.0 and the wildcard mask 0.0.3.255, the form Cisco access lists take. IPv6 is written with the prefix length alone, so both are given for IPv4 only.

How many can I convert at once?

Up to 1,000 at a time. One per line works, and commas, spaces, quotes and brackets separate entries too, so a JSON array or a CSV column pastes as it is. Copy puts the results on the clipboard tab-separated, ready for a spreadsheet; Export downloads them as CSV.

Is what I paste sent anywhere?

Not to convert it: that happens in your browser, with no lookup and nothing counted against an allowance. A batch that fits is kept in the page's address so the result can be shared, and opening that link sends it to us like any other URL.

HomeCIDR to IP Range

Tool

CIDR to IP Range Converter

Paste CIDR blocks or single addresses, IPv4 or IPv6, and get each one's first and last address and its exact size, with the netmask and wildcard mask for IPv4. Every address links to its own record, and every IPv4 block to the range page that holds it.

Results

CIDR	FIRST ADDRESS	LAST ADDRESS	ADDRESSES	NETMASK	WILDCARD	COVERAGE
192.168.100.0/22	First address192.168.100.0	Last address192.168.103.255	Addresses1,024	Netmask255.255.252.0	Wildcard0.0.3.255	Coverage192.168.0.0/16

How CIDR notation works

A CIDR block is an address and a prefix length. The prefix length counts the leading bits that name the network; the bits after it number the addresses inside it. 192.168.100.0/22 fixes the first 22 of its 32 bits, which leaves 10 bits, or 1,024 addresses, running from 192.168.100.0 to 192.168.103.255.

First11000000.10101000.01100100.00000000192.168.100.0

Last11000000.10101000.01100111.11111111192.168.103.255

Netmask11111111.11111111.11111100.00000000255.255.252.0

The 22 network bits in black, the 10 host bits in blue. The first address sets every host bit to 0, the last sets every one to 1, and the netmask is 22 ones followed by zeros.

IPv6 works the same way over 128 bits, and is written with the prefix length alone, so it has no netmask or wildcard here. A /64 holds 18,446,744,073,709,551,616 addresses, which is why counts are given in full rather than rounded.

Every IPv4 block in the results links to the /8, /16 or /24 page that holds it: where the block is, who announces it, and what each of our databases holds in it. All IP ranges starts from the top, and the bogon ranges are the blocks that never appear on the public internet. Convert 192.168.100.0/22 to see the example above in the converter.

Questions.

Read the docs →API reference →Email support →

On this page

What does the number after the slash mean?

It's the prefix length: how many leading bits of the address name the network. The rest number the addresses inside it, so a /24 holds 256 addresses, and a /32 or a /128 is a single address.

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