IPv4 Address (Strict 0–255) Regex for Go

What this pattern does

Need to validate IPv4 addresses with exacting precision in your Go application? This page offers a robust regular expression solution, specifically designed to match IPv4 addresses and ensure each octet falls within the 0–255 range. This regex will reject invalid formats and out-of-range values, making it ideal for network configuration tools or any Go project requiring strict IPv4 address validation. Employ it directly in your Go code, whether you are building a CLI, a web server, or a data processing pipeline.

Go Implementation

// IPv4 Address (Strict 0–255)
// ReDoS-safe | RegexVault — Web & Network > IPv4

package validation

import "regexp"

var ipv4AddressStrict0255Re = regexp.MustCompile(`^(?:(?:25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])\.){3}(?:25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])$`)

func ValidateIpv4AddressStrict0255(s string) bool {
    return ipv4AddressStrict0255Re.MatchString(s)
}

// Example
// fmt.Println(ValidateIpv4AddressStrict0255("0.0.0.0")) // true

Test Cases

When to use this pattern

Go's RE2 engine prevents catastrophic backtracking, so this pattern is already safe from a ReDoS perspective. However, using a verified pattern is still crucial. A carefully constructed regex minimizes the risk of unexpected behavior or performance degradation, especially with complex validation tasks. Imagine you're building a network monitoring tool in Go; using this verified pattern ensures that your application reliably parses and validates IPv4 addresses under heavy load, making it production-ready.

Common Pitfalls

Technical Notes

The alternation order in each octet group (25[0-5] first, then 2[0-4], then 1xx, then [1-9][0-9], then single digit) is critical for correctness. Reordering breaks range enforcement. Leading zeros are rejected because 01 does not match any branch.