IPv6 with CIDR Prefix Length Regex for PHP

What this pattern does

This page provides a well-structured, multi-part regular expression for matching ipv6 with cidr prefix length, ported and verified for PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. 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
// IPv6 with CIDR Prefix Length
// ReDoS-safe | RegexVault — Web & Network > IPv6

define('IPV6_WITH_CIDR_PREFIX_LENGTH_PATTERN', '/^[0-9a-fA-F:]+\\/(?:12[0-8]|1[01][0-9]|[1-9][0-9]|[0-9])$/');

function validate_ipv6_with_cidr_prefix_length(string $input): bool {
    return (bool) preg_match(IPV6_WITH_CIDR_PREFIX_LENGTH_PATTERN, $input);
}

// Example
var_dump(validate_ipv6_with_cidr_prefix_length("2001:db8::/32")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > IPv6 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

The IPv6 portion uses a simplified [0-9a-fA-F:]+ to avoid duplicating the full IPv6 validation. Pair with net-ipv6-02 for full address validation before applying this pattern.