IPv4 Address Validation Regex

Validate IPv4 addresses with proper octet range validation (0-255) using a comprehensive regex pattern.

Pattern Breakdown

^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)$

Components

Detailed Octet Breakdown

Each octet pattern (?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d) matches:

• 25[0-5] - 250-255
• 2[0-4]\d - 200-249
• 1\d\d - 100-199
• [1-9]\d - 10-99
• \d - 0-9

Examples

Valid:

• 192.168.1.1
• 10.0.0.1
• 255.255.255.255
• 0.0.0.0
• 172.16.0.1
• 8.8.8.8

Invalid:

• 256.1.1.1 (octet exceeds 255)
• 192.168.1 (only 3 octets)
• 192.168.1.1.1 (5 octets)
• 192.168.01.1 (leading zero, though format valid)
• 192.168.1 (incomplete)
• 192.168.1. (trailing dot)

Implementation

JavaScript

const ipv4Regex = /^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)$/;
ipv4Regex.test('192.168.1.1'); // true
ipv4Regex.test('255.255.255.255'); // true
ipv4Regex.test('0.0.0.0'); // true
ipv4Regex.test('256.1.1.1'); // false (exceeds 255)
ipv4Regex.test('192.168.1'); // false (incomplete)

Python

import re
ipv4_regex = r'^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)$'
bool(re.match(ipv4_regex, '192.168.1.1'))  # True
bool(re.match(ipv4_regex, '255.255.255.255'))  # True
bool(re.match(ipv4_regex, '256.1.1.1'))  # False (exceeds 255)

Go

ipv4Regex := regexp.MustCompile(`^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)$`)
ipv4Regex.MatchString("192.168.1.1") // true
ipv4Regex.MatchString("255.255.255.255") // true
ipv4Regex.MatchString("256.1.1.1") // false (exceeds 255)

Limitations

1. Leading zeros: Accepts 192.168.01.1 (technically valid format, but non-standard)
2. No reserved IP validation: Doesn't check for reserved/private IP ranges
3. Format only: Validates format, not network reachability
4. No CIDR support: Doesn't validate subnet masks (e.g., /24)
5. Complex pattern: Can be harder to read and maintain

When to Use

• IPv4 address format validation
• Network configuration forms
• IP input validation
• Firewall rule validation
• When you need strict octet range checking

For production, consider:

• Rejecting leading zeros for stricter validation
• Validating reserved/private IP ranges if needed
• Using IP parsing libraries for additional validation
• Supporting CIDR notation if required
• Combining with network reachability checks