CIDR / Subnet Calculator API

IPv4 / IPv6 subnet calculator: network, broadcast, netmask, host range and count; check if IPs are inside, split subnets, merge lists, range to CIDR.

GETPOSThttps://apibox.io.vn/v1/cidr

Network & Validation▶ Try it online

Give a network as cidr (192.168.1.0/24, 10.0.0.1/255.255.255.0, 2001:db8::/48) and get the network and broadcast address, netmask and wildcard mask, first / last address and usable host range, total addresses and usable hosts (RFC 3021 /31 and /32 handled), binary mask, class, address type (private, CGNAT, documentation, multicast…), the reverse DNS zone and the previous / next networks of the same size. IPv6 addresses are shown compressed and expanded, with the number of /64 subnets.

Other actions (chosen from the parameters, or with action): contains checks whether one or many ip (addresses or CIDRs) are inside the network; split cuts it into subnets by new prefix, number of subnets or hosts per subnet (up to 4096 listed); range turns first-last into the smallest list of CIDR blocks; merge takes a list of CIDRs, addresses and ranges (up to 10,000), merges overlapping and adjacent blocks into the minimal set and reports duplicates and overlaps.

Pure calculation with 128-bit integers: no lookup, nothing stored. For the owner and location of an address use /v1/ip, for cloud and Tor ranges /v1/ip-intel.

Parameters

Name	In	Type	Required	Default
`cidr`	query\|body	string	no		Network (`10.0.0.0/8`, `10.1.2.3/255.0.0.0`, `2001:db8::/32`), a single address, or `first-last` for action=range. Also in the path: /v1/cidr/10.0.0.0%2F8.
`action`	query\|body	string	no		`info`, `contains`, `split`, `range` or `merge` (guessed from the other parameters when absent).
`ip`	query\|body	string	no		contains: address(es) or CIDR(s) to test, comma or newline separated (up to 1000).
`prefix`	query\|body	number	no		split: new prefix length.
`subnets`	query\|body	number	no		split: number of subnets wanted (rounded up to a power of two).
`hosts`	query\|body	number	no		split: hosts needed per subnet.
`limit`	query\|body	number	no	`256`	split: subnets listed (1-4096).
`list`	body\|query	array	no		merge: CIDRs, addresses and ranges a-b (array or separated by new lines, commas, spaces), up to 10,000.

Example

curl "https://apibox.io.vn/v1/cidr?cidr=192.168.10.0/26" \
  -H "Authorization: Bearer YOUR_API_KEY"

const res = await fetch('https://apibox.io.vn/v1/cidr?cidr=192.168.10.0/26', {
  method: 'GET',
  headers: {
    Authorization: 'Bearer YOUR_API_KEY',
  },
});
const data = await res.json();
console.log(data);

import requests

res = requests.get(
    "https://apibox.io.vn/v1/cidr?cidr=192.168.10.0/26",
    headers={"Authorization": "Bearer YOUR_API_KEY"},
    timeout=30,
)
print(res.json())

<?php
$ch = curl_init('https://apibox.io.vn/v1/cidr?cidr=192.168.10.0/26');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => ['Authorization: Bearer YOUR_API_KEY'],
]);
$response = curl_exec($ch);
print_r(json_decode($response, true));

Response

{
  "action": "info",
  "cidr": "192.168.10.0/26",
  "version": 4,
  "prefix": 26,
  "network": "192.168.10.0",
  "netmask": "255.255.255.192",
  "wildcard": "0.0.0.63",
  "broadcast": "192.168.10.63",
  "first_address": "192.168.10.0",
  "last_address": "192.168.10.63",
  "first_host": "192.168.10.1",
  "last_host": "192.168.10.62",
  "total_addresses": 64,
  "usable_hosts": 62,
  "netmask_binary": "11111111.11111111.11111111.11000000",
  "network_hex": "0xc0a80a00",
  "integer_range": [
    3232238080,
    3232238143
  ],
  "class": "C",
  "type": "private",
  "reverse_zone": "10.168.192.in-addr.arpa",
  "previous_network": "192.168.9.192/26",
  "next_network": "192.168.10.64/26"
}

Use cases

Plan VPC subnets and VLANs (split a /16 into /24 blocks)
Clean and merge firewall or allowlist CIDR lists
Check whether client IPs fall inside an office or partner range
Convert IP ranges from logs or registries into CIDR notation

FAQ

How are /31 and /32 handled?

A /31 has two usable addresses (RFC 3021, point-to-point links) and no broadcast; a /32 is a single host.

What if the address has host bits set?

The network is computed from it (192.168.1.130/26 → 192.168.1.128/26) and the input address is shown with a note.

Is IPv6 supported everywhere?

Yes: info, contains, split, range and merge all work with IPv6, and lists can mix IPv4 and IPv6.

CIDR / Subnet Calculator API

Parameters

Example

Response

Use cases

FAQ

Related APIs

IP Geolocation

DNS Lookup

Email Validator