Private / Reserved IPv4 Ranges Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching private / reserved ipv4 ranges, ported and verified for PHP. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// Private / Reserved IPv4 Ranges
// ReDoS-safe | RegexVault — Security > Network Security

define('PRIVATE_RESERVED_IPV4_RANGES_PATTERN', '/^(?:10\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|172\.(?:1[6-9]|2[0-9]|3[01])\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|192\.168\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|127\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|169\.254\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))$/');

function validate_private_reserved_ipv4_ranges(string $input): bool {
    return (bool) preg_match(PRIVATE_RESERVED_IPV4_RANGES_PATTERN, $input);
}

// Example
var_dump(validate_private_reserved_ipv4_ranges("10.0.0.1")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Security > Network Security category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Private ranges: 10.0.0.0/8 (Class A, RFC 1918), 172.16.0.0/12 (Class B, RFC 1918), 192.168.0.0/16 (Class C, RFC 1918), 127.0.0.0/8 (loopback), 169.254.0.0/16 (link-local APIPA). Use for SSRF protection: reject private IPs in user-supplied URLs.