GitHub - brandonburrus/cidr-block: npm package for working with IPv4 and IPv6 addresses and CIDRs 📡

IPv4 and IPv6 address and CIDR range utilities for JavaScript and TypeScript.

Installation

npm install cidr-block

Features

Full IPv4 and IPv6 address support
CIDR block creation and manipulation
Address validation and parsing
Network calculations (netmask, hostmask, address count, usable addresses)
Subnetting operations
Address type detection (private, loopback, multicast, etc.)
Full TypeScript support with comprehensive type definitions
Zero dependencies
Works with ESM and CommonJS

Quick Start

import { ipv4, ipv6 } from 'cidr-block';

// Create and work with IPv4 addresses
const addr = ipv4.address('192.168.1.1');
console.log(addr.isPrivateAddress()); // true

// Create and work with CIDR blocks
const cidr = ipv4.cidr('10.0.0.0/16');
console.log(cidr.addressCount()); // 65536

// IPv6 works the same way
const v6addr = ipv6.address('2001:db8::1');
console.log(v6addr.toString()); // "2001:db8::1"

API Reference

Full documentation can be found at cidr-block.com.

IPv4

Creating Addresses

import { ipv4 } from 'cidr-block';

// From string
const addr1 = ipv4.address('192.168.1.1');

// From number
const addr2 = ipv4.address(3232235777);

// From octet array
const addr3 = ipv4.address([192, 168, 1, 1]);

Address Validation

import { ipv4 } from 'cidr-block';

ipv4.isValidAddress('192.168.1.1');     // true
ipv4.isValidAddress('256.1.1.1');       // false
ipv4.isValidAddress([10, 0, 0, 1]);     // true
ipv4.isValidAddress(4294967295);        // true (255.255.255.255)
ipv4.isValidAddress(4294967296);        // false (exceeds max)

Address Conversion

import { ipv4 } from 'cidr-block';

const addr = ipv4.address('192.168.1.1');

addr.toString();       // "192.168.1.1"
addr.toNumber();       // 3232235777
addr.octets();         // [192, 168, 1, 1]
addr.toBinaryString(); // "11000000.10101000.00000001.00000001"

Address Type Detection

import { ipv4 } from 'cidr-block';

// Private addresses (RFC 1918)
ipv4.address('10.0.0.1').isPrivateAddress();      // true
ipv4.address('172.16.0.1').isPrivateAddress();    // true
ipv4.address('192.168.0.1').isPrivateAddress();   // true
ipv4.address('8.8.8.8').isPrivateAddress();       // false

// Loopback addresses
ipv4.address('127.0.0.1').isLoopbackAddress();    // true
ipv4.address('127.255.255.255').isLoopbackAddress(); // true

// Link-local addresses
ipv4.address('169.254.1.1').isLocalLinkAddress(); // true

// Multicast addresses
ipv4.address('224.0.0.1').isMulticastAddress();   // true
ipv4.address('239.255.255.255').isMulticastAddress(); // true

Address Comparison

import { ipv4 } from 'cidr-block';

const addr1 = ipv4.address('192.168.1.1');
const addr2 = ipv4.address('192.168.1.2');

addr1.equals('192.168.1.1');           // true
addr1.equals(addr2);                   // false
addr1.isLessThan(addr2);               // true
addr1.isGreaterThan(addr2);            // false
addr1.isLessThanOrEqual(addr2);        // true
addr1.isGreaterThanOrEqual(addr2);     // false

Address Navigation

import { ipv4 } from 'cidr-block';

const addr = ipv4.address('192.168.1.100');

addr.hasNextAddress();       // true
addr.nextAddress()?.toString();    // "192.168.1.101"

addr.hasPreviousAddress();   // true
addr.previousAddress()?.toString(); // "192.168.1.99"

// Edge cases
const maxAddr = ipv4.address('255.255.255.255');
maxAddr.hasNextAddress();    // false
maxAddr.nextAddress();       // undefined

const minAddr = ipv4.address('0.0.0.0');
minAddr.hasPreviousAddress(); // false
minAddr.previousAddress();    // undefined

Creating CIDR Blocks

import { ipv4 } from 'cidr-block';

// From string
const cidr1 = ipv4.cidr('192.168.0.0/24');

// From object
const cidr2 = ipv4.cidr({ address: '192.168.0.0', range: 24 });

// From tuple
const cidr3 = ipv4.cidr(['192.168.0.0', 24]);

// Mixed formats work too
const cidr4 = ipv4.cidr({ address: [192, 168, 0, 0], range: 24 });

CIDR Validation

import { ipv4 } from 'cidr-block';

ipv4.isValidCIDR('192.168.0.0/24');   // true
ipv4.isValidCIDR('192.168.0.0/33');   // false (range exceeds 32)
ipv4.isValidCIDR('256.0.0.0/24');     // false (invalid address)
ipv4.isValidCIDR(['10.0.0.0', 8]);    // true

CIDR Properties

import { ipv4 } from 'cidr-block';

const cidr = ipv4.cidr('192.168.0.0/24');

cidr.toString();                  // "192.168.0.0/24"
cidr.baseAddress().toString();    // "192.168.0.0"
cidr.range();                     // 24
cidr.netmask().toString();        // "255.255.255.0"
cidr.hostmask().toString();       // "0.0.0.255"
cidr.addressCount();              // 256
cidr.rangeParts();                // [Ipv4Address, 24]

// Calculate network address from CIDR with host bits
const hostCidr = ipv4.cidr('192.168.1.5/24');
hostCidr.network().toString();      // "192.168.1.0"
hostCidr.networkCIDR().toString();  // "192.168.1.0/24"

Usable Addresses

import { ipv4 } from 'cidr-block';

const cidr = ipv4.cidr('192.168.1.0/24');

// First usable (excludes network address)
cidr.getFirstUsableAddress()?.toString(); // "192.168.1.1"

// Last usable (excludes broadcast address)
cidr.getLastUsableAddress()?.toString();  // "192.168.1.254"

// For /32, there are no usable addresses
const hostCidr = ipv4.cidr('192.168.1.1/32');
hostCidr.getFirstUsableAddress(); // undefined
hostCidr.getLastUsableAddress();  // undefined

Iterating Addresses

import { ipv4 } from 'cidr-block';

const cidr = ipv4.cidr('192.168.1.0/30');

// Using the generator
for (const addr of cidr.addresses()) {
  console.log(addr.toString());
}
// Output:
// 192.168.1.0
// 192.168.1.1
// 192.168.1.2
// 192.168.1.3

// Convert to array
const allAddresses = [...cidr.addresses()];
console.log(allAddresses.length); // 4

Address Containment

import { ipv4 } from 'cidr-block';

const cidr = ipv4.cidr('192.168.0.0/24');

cidr.includes(ipv4.address('192.168.0.100')); // true
cidr.includes(ipv4.address('192.168.1.1'));   // false
cidr.includes(ipv4.address('192.168.0.0'));   // true
cidr.includes(ipv4.address('192.168.0.255')); // true

CIDR Overlap Detection

import { ipv4 } from 'cidr-block';

const cidr1 = ipv4.cidr('192.168.0.0/24');
const cidr2 = ipv4.cidr('192.168.0.128/25');
const cidr3 = ipv4.cidr('192.168.1.0/24');

cidr1.overlaps(cidr2); // true (cidr2 is a subnet of cidr1)
cidr1.overlaps(cidr3); // false (different networks)

// Also accepts string format
cidr1.overlaps('10.0.0.0/8'); // false

Subnetting

import { ipv4 } from 'cidr-block';

const cidr = ipv4.cidr('192.168.0.0/24');

// Split into equal subnets
const subnets = cidr.subnet(26);
subnets.forEach(s => console.log(s.toString()));
// Output:
// 192.168.0.0/26
// 192.168.0.64/26
// 192.168.0.128/26
// 192.168.0.192/26

// Split into variable-sized subnets
const varSubnets = cidr.subnetBy([26, 27, 27, 26]);
varSubnets.forEach(s => console.log(s.toString()));
// Output:
// 192.168.0.0/26
// 192.168.0.64/27
// 192.168.0.96/27
// 192.168.0.128/26

CIDR Navigation

import { ipv4 } from 'cidr-block';

const cidr = ipv4.cidr('192.168.0.0/24');

cidr.hasNextCIDR();                    // true
cidr.nextCIDR()?.toString();           // "192.168.1.0/24"

cidr.hasPreviousCIDR();                // true
cidr.previousCIDR()?.toString();       // "192.167.255.0/24"

IPv6

Creating Addresses

import { ipv6 } from 'cidr-block';

// From string (with :: compression)
const addr1 = ipv6.address('2001:db8::1');

// From full string
const addr2 = ipv6.address('2001:0db8:0000:0000:0000:0000:0000:0001');

// From BigInt
const addr3 = ipv6.address(42540766411282592856903984951653826561n);

// From hextets array
const addr4 = ipv6.address([0x2001, 0x0db8, 0, 0, 0, 0, 0, 1]);

Address Validation

import { ipv6 } from 'cidr-block';

ipv6.isValidAddress('2001:db8::1');           // true
ipv6.isValidAddress('::1');                   // true
ipv6.isValidAddress('::');                    // true
ipv6.isValidAddress('::ffff:192.168.1.1');    // true (IPv4-mapped)
ipv6.isValidAddress('2001:db8::g');           // false (invalid hex)
ipv6.isValidAddress('2001:db8:::1');          // false (multiple ::)

Address Conversion

import { ipv6 } from 'cidr-block';

const addr = ipv6.address('2001:db8::1');

addr.toString();     // "2001:db8::1" (compressed)
addr.toFullString(); // "2001:0db8:0000:0000:0000:0000:0000:0001"
addr.toBigInt();     // 42540766411282592856903984951653826561n
addr.hextets();      // [8193, 3512, 0, 0, 0, 0, 0, 1]
addr.toBinaryString(); // Binary representation with colons

Address Type Detection

import { ipv6 } from 'cidr-block';

// Loopback
ipv6.address('::1').isLoopbackAddress();          // true

// Unspecified
ipv6.address('::').isUnspecifiedAddress();        // true

// Unique local (private equivalent)
ipv6.address('fc00::1').isUniqueLocalAddress();   // true
ipv6.address('fd00::1').isUniqueLocalAddress();   // true

// Link-local
ipv6.address('fe80::1').isLinkLocalAddress();     // true

// Multicast
ipv6.address('ff02::1').isMulticastAddress();     // true

// IPv4-mapped
ipv6.address('::ffff:192.168.1.1').isIPv4MappedAddress(); // true

// Documentation
ipv6.address('2001:db8::1').isDocumentationAddress(); // true

Address Comparison

import { ipv6 } from 'cidr-block';

const addr1 = ipv6.address('2001:db8::1');
const addr2 = ipv6.address('2001:db8::2');

addr1.equals('2001:db8::1');           // true
addr1.equals(addr2);                   // false
addr1.isLessThan(addr2);               // true
addr1.isGreaterThan(addr2);            // false
addr1.isLessThanOrEqual(addr2);        // true
addr1.isGreaterThanOrEqual(addr2);     // false

Address Navigation

import { ipv6 } from 'cidr-block';

const addr = ipv6.address('2001:db8::1');

addr.hasNextAddress();                // true
addr.nextAddress()?.toString();       // "2001:db8::2"

addr.hasPreviousAddress();            // true
addr.previousAddress()?.toString();   // "2001:db8::"

Creating CIDR Blocks

import { ipv6 } from 'cidr-block';

// From string
const cidr1 = ipv6.cidr('2001:db8::/32');

// From object
const cidr2 = ipv6.cidr({ address: '2001:db8::', range: 32 });

// From tuple
const cidr3 = ipv6.cidr(['2001:db8::', 32]);

CIDR Validation

import { ipv6 } from 'cidr-block';

ipv6.isValidCIDR('2001:db8::/32');    // true
ipv6.isValidCIDR('2001:db8::/129');   // false (range exceeds 128)
ipv6.isValidCIDR(['::1', 128]);       // true

CIDR Properties

import { ipv6 } from 'cidr-block';

const cidr = ipv6.cidr('2001:db8::/32');

cidr.toString();                  // "2001:db8::/32"
cidr.baseAddress().toString();    // "2001:db8::"
cidr.range();                     // 32
cidr.netmask().toString();        // "ffff:ffff::"
cidr.hostmask().toString();       // "::ffff:ffff:ffff:ffff:ffff:ffff"
cidr.addressCount();              // 79228162514264337593543950336n (BigInt)

// Calculate network address from CIDR with host bits
const hostCidr = ipv6.cidr('2001:db8::1234/32');
hostCidr.network().toString();      // "2001:db8::"
hostCidr.networkCIDR().toString();  // "2001:db8::/32"

Usable Addresses

import { ipv6 } from 'cidr-block';

const cidr = ipv6.cidr('2001:db8::/126');

cidr.getFirstUsableAddress()?.toString(); // "2001:db8::1"
cidr.getLastUsableAddress()?.toString();  // "2001:db8::2"

// For /128, there are no usable addresses
const hostCidr = ipv6.cidr('2001:db8::1/128');
hostCidr.getFirstUsableAddress(); // undefined
hostCidr.getLastUsableAddress();  // undefined

Iterating Addresses

import { ipv6 } from 'cidr-block';

const cidr = ipv6.cidr('2001:db8::/126');

for (const addr of cidr.addresses()) {
  console.log(addr.toString());
}
// Output:
// 2001:db8::
// 2001:db8::1
// 2001:db8::2
// 2001:db8::3

// With limit (useful for large ranges)
for (const addr of cidr.addresses(2n)) {
  console.log(addr.toString());
}
// Output:
// 2001:db8::
// 2001:db8::1

Address Containment and Overlap

import { ipv6 } from 'cidr-block';

const cidr = ipv6.cidr('2001:db8::/32');

cidr.includes(ipv6.address('2001:db8::1'));      // true
cidr.includes(ipv6.address('2001:db9::1'));      // false

const cidr2 = ipv6.cidr('2001:db8:1::/48');
cidr.overlaps(cidr2);  // true

Subnetting

import { ipv6 } from 'cidr-block';

const cidr = ipv6.cidr('2001:db8::/32');

// Split into /34 subnets
const subnets = cidr.subnet(34);
subnets.forEach(s => console.log(s.toString()));
// Output:
// 2001:db8::/34
// 2001:db8:4000::/34
// 2001:db8:8000::/34
// 2001:db8:c000::/34

// Variable-sized subnets
const varSubnets = cidr.subnetBy([34, 34, 33]);
varSubnets.forEach(s => console.log(s.toString()));

CIDR Navigation

import { ipv6 } from 'cidr-block';

const cidr = ipv6.cidr('2001:db8::/32');

cidr.hasNextCIDR();                  // true
cidr.nextCIDR()?.toString();         // "2001:db9::/32"

cidr.hasPreviousCIDR();              // true
cidr.previousCIDR()?.toString();     // "2001:db7::/32"

Error Handling

import {
  ipv4,
  ipv6,
  InvalidIpv4AddressError,
  InvalidIpv4CidrError,
  InvalidIpv4CidrRangeError,
  InvalidIpv6AddressError,
  InvalidIpv6CidrError,
  InvalidIpv6CidrRangeError
} from 'cidr-block';

// Invalid address throws error
try {
  ipv4.address('256.0.0.1');
} catch (e) {
  if (e instanceof InvalidIpv4AddressError) {
    console.log(e.message); // "256.0.0.1 is not a valid IPv4 address"
  }
}

// Invalid CIDR throws error
try {
  ipv4.cidr('192.168.0.0/33');
} catch (e) {
  if (e instanceof InvalidIpv4CidrError) {
    console.log(e.message); // "192.168.0.0/33 is not a valid IPv4 CIDR range"
  }
}

// Invalid subnet operation throws error
try {
  const cidr = ipv4.cidr('192.168.0.0/24');
  cidr.subnet(20); // Can't create larger subnets
} catch (e) {
  if (e instanceof InvalidIpv4CidrRangeError) {
    console.log('Invalid subnet range');
  }
}

// Use validation to avoid exceptions
if (ipv4.isValidAddress(userInput)) {
  const addr = ipv4.address(userInput);
  // Safe to use
}

Constants

import { ipv4, ipv6 } from 'cidr-block';

// IPv4 constants
ipv4.MAX_SIZE;   // 0xffffffff (4294967295)
ipv4.MIN_SIZE;   // 0x00000000
ipv4.MAX_RANGE;  // 32
ipv4.MIN_RANGE;  // 0

// IPv6 constants
ipv6.MAX_SIZE;   // (1n << 128n) - 1n
ipv6.MIN_SIZE;   // 0n
ipv6.MAX_RANGE;  // 128
ipv6.MIN_RANGE;  // 0

Type Definitions

import type {
  // IPv4 types
  Ipv4AddressLiteral,  // string | number | number[]
  Ipv4AddressString,   // "${number}.${number}.${number}.${number}"
  Ipv4AddressOctets,   // [number, number, number, number]
  Ipv4CidrLiteral,     // string | { address, range } | [address, range]
  Ipv4CidrString,      // "${number}.${number}.${number}.${number}/${number}"

  // IPv6 types
  Ipv6AddressLiteral,  // string | bigint | number[]
  Ipv6AddressHextets,  // [number, number, number, number, number, number, number, number]
  Ipv6CidrLiteral,     // string | { address, range } | [address, range]
} from 'cidr-block';

Common Use Cases

Checking if an IP is in a Private Network

import { ipv4 } from 'cidr-block';

function isInternalIP(ip: string): boolean {
  if (!ipv4.isValidAddress(ip)) return false;
  const addr = ipv4.address(ip);
  return addr.isPrivateAddress() || addr.isLoopbackAddress();
}

isInternalIP('192.168.1.1');  // true
isInternalIP('10.0.0.1');     // true
isInternalIP('8.8.8.8');      // false

Allocating Subnets from a Pool

import { ipv4 } from 'cidr-block';

function allocateSubnets(poolCidr: string, subnetSize: number, count: number) {
  const pool = ipv4.cidr(poolCidr);
  const subnets = pool.subnet(subnetSize);
  return subnets.slice(0, count);
}

const allocated = allocateSubnets('10.0.0.0/16', 24, 3);
allocated.forEach(s => console.log(s.toString()));
// 10.0.0.0/24
// 10.0.1.0/24
// 10.0.2.0/24

Checking for CIDR Conflicts

import { ipv4, Ipv4Cidr } from 'cidr-block';

function findConflicts(newCidr: string, existing: string[]): string[] {
  const cidr = ipv4.cidr(newCidr);
  return existing.filter(e => cidr.overlaps(e));
}

const existingRanges = ['10.0.0.0/24', '10.0.1.0/24', '192.168.0.0/16'];
const conflicts = findConflicts('10.0.0.0/16', existingRanges);
// ['10.0.0.0/24', '10.0.1.0/24']

Generating IP Addresses in a Range

import { ipv4 } from 'cidr-block';

function getUsableIPs(cidrStr: string): string[] {
  const cidr = ipv4.cidr(cidrStr);
  const ips: string[] = [];

  for (const addr of cidr.addresses()) {
    // Skip network and broadcast addresses for practical use
    if (addr.equals(cidr.baseAddress())) continue;

    const lastOctet = addr.octets()[3];
    if (lastOctet === 255) continue; // Skip broadcast

    ips.push(addr.toString());
  }

  return ips;
}

const usable = getUsableIPs('192.168.1.0/29');
// ['192.168.1.1', '192.168.1.2', '192.168.1.3', '192.168.1.4', '192.168.1.5', '192.168.1.6']

Normalizing CIDR Blocks

import { ipv4, ipv6 } from 'cidr-block';

// Normalize IPv4 CIDR by removing host bits
function normalizeIPv4CIDR(cidrStr: string): string {
  const cidr = ipv4.cidr(cidrStr);
  return cidr.networkCIDR().toString();
}

normalizeIPv4CIDR('192.168.1.5/24');    // "192.168.1.0/24"
normalizeIPv4CIDR('10.5.10.20/8');      // "10.0.0.0/8"
normalizeIPv4CIDR('172.16.50.100/12');  // "172.16.0.0/12"

// Normalize IPv6 CIDR by removing host bits
function normalizeIPv6CIDR(cidrStr: string): string {
  const cidr = ipv6.cidr(cidrStr);
  return cidr.networkCIDR().toString();
}

normalizeIPv6CIDR('2001:db8::1234/32');                   // "2001:db8::/32"
normalizeIPv6CIDR('2001:db8:1:2:3:4:5:6/64');             // "2001:db8:1:2::/64"
normalizeIPv6CIDR('2001:db8:abcd:ef01::/48');             // "2001:db8:abcd::/48"

Name		Name	Last commit message	Last commit date
Latest commit History 36 Commits
src		src
tests		tests
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md
biome.json		biome.json
netlify.toml		netlify.toml
package-lock.json		package-lock.json
package.json		package.json
rollup.config.js		rollup.config.js
tsconfig.json		tsconfig.json
typedoc.json		typedoc.json
vitest.config.ts		vitest.config.ts

Folders and files

Latest commit

History

Repository files navigation

Installation

Features

Quick Start

API Reference

IPv4

Creating Addresses

Address Validation

Address Conversion

Address Type Detection

Address Comparison

Address Navigation

Creating CIDR Blocks

CIDR Validation

CIDR Properties

Usable Addresses

Iterating Addresses

Address Containment

CIDR Overlap Detection

Subnetting

CIDR Navigation

IPv6

Creating Addresses

Address Validation

Address Conversion

Address Type Detection

Address Comparison

Address Navigation

Creating CIDR Blocks

CIDR Validation

CIDR Properties

Usable Addresses

Iterating Addresses

Address Containment and Overlap

Subnetting

CIDR Navigation

Error Handling

Constants

Type Definitions

Common Use Cases

Checking if an IP is in a Private Network

Allocating Subnets from a Pool

Checking for CIDR Conflicts

Generating IP Addresses in a Range

Normalizing CIDR Blocks

About

Topics

Resources

License

Uh oh!

Stars

Watchers

Forks

Releases 10

Uh oh!

Contributors

Uh oh!

Languages