Regex for IPv4 Address — Pattern Explained with Examples

In this tutorial, you'll learn about Regex for IPv4 Address. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

IPv4 address validation is fundamental for network configuration tools, security scanners, and any application that handles IP-based communication. Each IPv4 address consists of four octets ranging from 0 to 255, separated by dots. A simple pattern checks the format, while a complete pattern enforces the 0-255 range.

The Pattern

/^(\d{1,3}\.){3}\d{1,3}$/

For strict 0-255 octet validation:

/^(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)$/

Pattern Breakdown

Matches

• 192.168.1.1
• 10.0.0.1
• 255.255.255.255
• 0.0.0.0
• 8.8.8.8

Does NOT Match

• 256.1.2.3 (octet out of range)
• 192.168.1 (only 3 octets)
• 192.168.1.1.1 (5 octets)
• 192.168.1.abc (non-numeric)
• .0.0.1 (leading dot)
• 999.999.999.999 (all octets out of range)

Language Examples

JavaScript

const ipv4Regex = /^(\d{1,3}\.){3}\d{1,3}$/;
const strictIpv4Regex = /^(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)$/;
console.log(strictIpv4Regex.test('192.168.1.1')); // true
console.log(strictIpv4Regex.test('256.1.2.3'));   // false

Python

import re
pattern = r'^(\d{1,3}\.){3}\d{1,3}$'
print(bool(re.match(pattern, '192.168.1.1')))  # True
print(bool(re.match(pattern, '256.1.2.3')))    # True (simple pattern allows it)

strict = r'^(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.(25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)$'
print(bool(re.match(strict, '256.1.2.3')))     # False

Rust

use regex::Regex;

fn main() {
    let re = Regex::new(r"^(\d{1,3}\.){3}\d{1,3}$").unwrap();
    println!("{}", re.is_match("192.168.1.1")); // true
}

Common Pitfalls

• The simple \d{1,3} pattern accepts numbers 000-999, so 999.999.999.999 passes format checks. Always use the full 0-255 pattern for strict validation
• Leading zeros are valid (e.g. 192.168.001.001 is a legitimate IPv4 address), but some applications reject them
• Partial matches within larger text (e.g. matching 192.168.1.1 inside http://192.168.1.1:8080/path) require lookarounds or separate tokenization
• CIDR notation (e.g. 192.168.1.0/24) is a separate concept — the mask after the slash needs its own validation

Real-World Use Cases

• Network configuration forms — validate static IP entries in router or server admin panels
• Log analysis tools — extract and validate IP addresses from access logs for geo-location or threat detection
• Access control lists — verify IP address entries in firewall rules or allowlist configurations

FAQ

Related Patterns

Regex for IPv6 Address Regex for MAC Address