range_check

Range Check v4.1.0

 

This is a simple module to validate IP address, check IP address version, check if IP is within a range.

This started out as range_check but it does much more than just checking ranges but since it's already got a large amount of downloads (37,115 downloads in the last month as of this writing) I'll keep the name the same even though I kinda want to change it to something better.

Table of Contents

• Install
• IP Functions
  • Check if IP is valid
  • Check IP version
    • Version
    • isV4
    • isV6
• Range Functions
  • Check if range is valid
  • Check if IP is within range
  • Check if IP is private
  • Check if IP is in range or private
  • IP Fingerprinting
  • storeIP
  • searchIP
  • displayIP
• Contributing
• Dependencies

Install

npm install range_check or yarn add range_check

You can then import the functions as needed or require the entire range_check package depending on your own projects configuration.

IP Functions

Check if IP is valid

console.log(isIP('10.0.1.5')); //returns true or false

Check IP version

Version

console.log(version('10.0.1.5')); //returns 4
console.log(version('2001:4860:8006::62')); //returns 6
console.log(version('foo')); //returns 0 as invalid IP address

isV4

console.log(isV4('10.0.1.5')); //true
console.log(isV4('foo')); //false
console.log(isV4('123::123')); //false

isV6

console.log(isV6('123::123')); //true
console.log(isV6('foo')); //false
console.log(isV6('10.0.1.5')); //false

Range Functions

Check if range is valid

You can use isRange if you want to validate an entire range.

console.log(isRange('2001:db8::/32')); //true
console.log(isRange('10.0.0.0/8')); // true
console.log(isRange('qwerty')); // false

Check if IP is within range

console.log(inRange('10.0.1.5', '10.0.0.0/8')); //returns true

console.log(inRange('192.0.1.5', '10.0.0.0/8')); //returns false

console.log(inRange('2001:db8:1234::1', '2001:db8::/32')); //returns true

You can also give a list of ranges

console.log(inRange('192.168.1.1', ['10.0.0.0/8', '192.0.0.0/8'])); //returns true

Check if IP is private

console.log(isPrivateIP('10.0.0.1')); //returns true
console.log(isPrivateIP('192.168.1.1')); //returns true
console.log(isPrivateIP('172.16.0.1')); //returns true
console.log(isPrivateIP('8.8.8.8')); //returns false
console.log(isPrivateIP('fd00::1')); //returns true (IPv6 ULA)
console.log(isPrivateIP('2001:db8::1')); //returns false
console.log(isPrivateIP('::ffff:192.168.1.1')); //returns true (IPv4-mapped IPv6 address to private IPv4)
console.log(isPrivateIP('::ffff:8.8.8.8')); //returns false (IPv4-mapped IPv6 address to public IPv4)

This function checks if an IP address is private. It returns true for:

• IPv4 private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
• IPv4 loopback addresses (127.0.0.0/8)
• IPv6 unique local addresses (fd00::/8)
• IPv6 loopback address (::1)
• IPv4-mapped IPv6 addresses that map to private IPv4 addresses (e.g., ::ffff:192.168.1.1)

Check if IP is in range or private

console.log(isIPInRangeOrPrivate('192.168.1.1')); // returns true (private IP)
console.log(isIPInRangeOrPrivate('8.8.8.8')); // returns false (public IP, no range specified)
console.log(isIPInRangeOrPrivate('8.8.8.8', { ranges: '8.8.8.0/24' })); // returns true
console.log(
  isIPInRangeOrPrivate('10.0.0.1', {
    allowAnyPrivate: false,
    ranges: '8.8.8.0/24',
  })
); // returns false

This function checks if an IP address is either within a specified range or is a private IP. It's particularly useful for scenarios where you need to determine if a request is coming from a local server or a specific set of allowed IPs.

Options:

• ranges: A string or array of strings representing IP ranges to check against.
• allowAnyPrivate: Boolean to determine if any private IP should be allowed. Defaults to true.

If no options are provided, the function will return true for any private IP and false for public IPs.

Use case example: This function can be used in server configurations to easily allow local calls or calls from specific IP ranges, while blocking others. For instance, it can be used in middleware for setting trace IDs. This allows you to automatically set trace IDs for requests from private networks or specific IP ranges, which can be useful for debugging and tracking requests across microservices in a distributed system.

IP Fingerprinting

The package provides two functions for generating IP address fingerprints:

Synchronous (unhashed) version

console.log(IPFingerprint('192.168.1.1')); // 'v4:192.168.1.1'
console.log(IPFingerprint('2001:db8::1')); // 'v6:2001:db8:0:0::'

This function generates a consistent fingerprint for IP addresses that can be used for bot tracking and analytics:

• For IPv4 addresses: Uses the full address
• For IPv6 addresses: Uses only the /64 network prefix (first 4 segments)

The function returns a string in the format v4:ADDRESS for IPv4 addresses or v6:PREFIX:: for IPv6 addresses.

Asynchronous (hashed) version

// Using async/await
const hashedFingerprint = await IPFingerprintHashed('192.168.1.1');
console.log(hashedFingerprint); // 'v4:a1e2f3...' (SHA-256 hash)

// Using Promises
IPFingerprintHashed('2001:db8::1')
  .then((fingerprint) => console.log(fingerprint)) // 'v6:a1e2f3...' (SHA-256 hash)
  .catch((error) => console.error(error));

This asynchronous function generates a hashed fingerprint using the Web Crypto API, which works in both modern browsers and Node.js/Bun environments. It applies a SHA-256 hash to the IP address part only (without the prefix) and then combines it with the original prefix. This means the format is still v4:HASH or v6:HASH, but only the actual IP address or subnet is used in the hash calculation.

Important: If the Web Crypto API is not available in the environment, this function will throw an error rather than silently falling back to an unhashed fingerprint. This ensures you're aware when the hashing functionality isn't working as expected.

Use cases

The IP fingerprinting functions are designed to address several common challenges in web applications:

1. Signup Rate Limiting and Abuse Prevention

// Example: Rate limiting signups from the same network
const ipKey = await IPFingerprintHashed(userIP);

// Use the fingerprint as a key in your rate limiting system
// This allows tracking signup attempts per network without storing actual IPs
if (tooManySignups(ipKey)) {
  throw new Error('Too many signup attempts from your network');
}

This approach effectively prevents mass signup abuse while respecting privacy. For IPv6 users, it only considers the /64 network prefix, which represents a single household or organization.

2. Content View Limiting

// Example: Limiting free article views for users from the same network
const viewKey = IPFingerprint(visitorIP); // Unhashed is fine for this use case

// Track views using the fingerprint as identifier
if (viewCountExceeded(articleId, viewKey)) {
  showPaywall();
}

This creates a persistent identifier for content views without storing the actual IP address.

3. Bot Detection and Security

// Example: Track failed login attempts without storing raw IPs
const hashedIp = await IPFingerprintHashed(clientIP);

// Track repeated failures from the same network
if (failedAttemptsExceeded(hashedIp)) {
  // Require CAPTCHA or temporarily block
  requireCaptcha();
}

Technical Considerations

The functions handle IPv6 addresses appropriately by using the /64 prefix. According to RFC 7421, the IPv6 addressing architecture uses a fixed boundary between the network prefix and the interface identifier at the /64 boundary. This standard reflects how IPv6 networks are deployed, with a /64 prefix typically representing a single subnet that might correspond to a household, small business, or organizational network.

This implementation aligns with privacy best practices described in RFC 8981, which discusses temporary address extensions for IPv6. While individual devices within a network might use temporary addresses that change over time (to prevent tracking of specific devices), the network prefix (/64) typically remains stable for a given network.

The hashed version adds an extra layer of privacy by making it impossible to reverse-engineer the original IP address from the fingerprint, which is particularly important for compliance with privacy regulations while still allowing effective rate limiting.

storeIP

This function is useful to get a consistent IP address such for storing it in a database or when searching in a database after being stored using this. So if a V6 address was sent compacted or not, or if you searched by either version this function would make sure you get a consistent IP address for both versions. Also the possibly of saving a few bytes.

If an V6 addressed is mapped as v4 is given it will convert it to V4, If any other V6 address is given it is abbreviated and plain V4 addresses are left alone. Returns null if a invalid IP

console.log(storeIP('foo')); //null
console.log(storeIP('::ffff:127.0.0.1')); //127.0.0.1
console.log(storeIP('2001:0000:0111:0000:0011:0000:0001:0000')); //2001:0:111:0:11:0:1:0
console.log(storeIP('2001:0001:0000:0001:0000:0000:0000:0000')); //2001:1:0:1::
console.log(storeIP('0000:0000:0000:0000:0000:0000:0000:0000')); //::
console.log(storeIP('0000:0000:0000:0000:0000:0000:0000:0001')); //::1
console.log(storeIP('2041:0000:140F:0000:0000:0000:875B:131B')); //2041:0:140F::875B:131B
console.log(storeIP('2001:0001:0002:0003:0004:0005:0006:0007')); //2001:1:2:3:4:5:6:7
console.log(storeIP('127.0.0.1')); //127.0.0.1

searchIP

Same function as storeIP, just a clearer name when you are using it for search instead

displayIP

This function is useful for displaying IP addresses, such as after grabbing it back from the database when using storeIP

If an V6 addressed mapped as v4 is given it will convert it to V4, If any other V6 address is given it is normalized into the longer version and plain V4 addresses are left alone. Returns a empty string if a invalid IP

console.log(displayIP(null)); // ''
console.log(displayIP('::ffff:127.0.0.1')); //'127.0.0.1'
console.log(displayIP('2001:0:111:0:11:0:1:0')); //'2001:0000:0111:0000:0011:0000:0001:0000'
console.log(displayIP('2001:1:0:1::')); //'2001:0001:0000:0001:0000:0000:0000:0000'
console.log(displayIP('::')); //'0000:0000:0000:0000:0000:0000:0000:0000'
console.log(displayIP('::1')); //'0000:0000:0000:0000:0000:0000:0000:0001'
console.log(displayIP('2041:0:140F::875B:131B')); //'2041:0000:140F:0000:0000:0000:875B:131B'
console.log(displayIP('2001:1:2:3:4:5:6:7')); //'2001:0001:0002:0003:0004:0005:0006:0007'
console.log(displayIP('127.0.0.1')); //'127.0.0.1'

Contributing

This project is using this starter library bun-lib-starter Currently to use NPM to publish, must have that installed with Node, along side Bun

cd into the repo

pre-commit install

bun install

• bun run test: Run test suite
• bun run build: Generate bundles and typings and updates README version
• bun run format: Format source files, readme, etc
• bun run update-version: Updates the version in README.md to match package.json

Version Management

When publishing a new version:

• Update the version in package.json
• Run bun test to run the test suite
• Run bun run build which will automatically update the version in README.md
• The version in README.md will be synchronized with package.json during the build process
• Run bun publish to publish the new version to NPM

Dependencies

• ipaddr.js - https://github.com/whitequark/ipaddr.js
• ip6 - https://github.com/elgs/ip6

Changelog

4.1.0 (May 26, 2025)

• Added IPFingerprint function for creating consistent fingerprints from IP addresses
  • For IPv4: Uses the full address
  • For IPv6: Uses only the /64 network prefix (first 4 segments)
• Added IPFingerprintHashed asynchronous function that creates SHA-256 hashed fingerprints
  • Uses Web Crypto API for cross-environment compatibility (browsers and Node.js/Bun)
  • Only hashes the IP address part, not the type prefix
• Both functions properly handle special cases:
  • IPv4-mapped IPv6 addresses
  • IPv6 ULA ranges (fd00::/8)
  • Loopback addresses (::1)
  • Documentation prefixes (2001:db8::/32)
  • Global unicast addresses