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is-in-subnet

Checking if an address is in a subnet

isInSubnet(address: string, subnetOrSubnets: string | string[]): boolean

Test if the given IP address is contained in the specified subnet.

ℹ️ check(…) is an alias for isInSubnet(…)

  • address the IPv4 or IPv6 address to check
  • subnet the IPv4 or IPv6 CIDR to test (or an array of them)

Will throw an Error if the address or subnet are not valid IP addresses, or the CIDR prefix length is not valid.

Or the functional version:

createChecker(subnetOrSubnets: string | string[]): (address: string) => boolean

Create a function from one or more subnet, to check an if an address belongs to any of them.

When checking many subnets together many times, it pays to amortise as much of the upfront processing as possible.

This functional version will throw an Error if the subnet(s) given are invalid, and the returned function will throw an if the given address is not valid.

Checking if a string represents a valid IP address

  • isIPv4(s: string): boolean

    • Test if the string represents an IPv4 address. Matches the similar function in Node.js: net.isIPv4

  • isIPv6(s: string): boolean

    • Test if the string represents an IPv6 address. Matches the similar function in Node.js: net.isIPv6

  • isIP(s: string): 0 | 4 | 6

    • Combined test that checks if the string represents either an IPv4 or IPv6 address. Returns 4 or 6 if the address can be parsed. If the address isn’t recognized as either IPv4 or IPv6, returns 0. Matches the similar function in Node.js: net.isIP

Testing for special address ranges

  • isPrivate(address: string): boolean

    • Test if the given IP address is a private/internal IP address. For IPv4 this includes 192.168.x.x and similar addresses. For IPv6 it includes link-local and ULA (unique local address) ranges.

  • isLocalhost(address: string): boolean

    • Test if the given IP address is a localhost address.

  • isReserved(address: string): boolean

    • Test if the given IP address is in a reserved range. This includes addresses that are not expected to be seen in public internet traffic, multicast, deprecated, and other special-use addresses.

  • isSpecial(address: string): boolean

    • A combined test that checks if the given IP address matches any of the above categories (private, localhost, or reserved).

The complete list can be seen in the source code: ipRange.ts