Regex for IPv4 Address — Pattern Explained with Examples

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