🔍Regex Recipes

IPv4 Address Validation

Strict IPv4 address validation ensuring each octet is 0-255.

Pattern

^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$

Explanation

Validates IPv4 addresses with strict octet validation (0-255). Each octet can be 1-3 digits.

Examples

Valid IP
Input
192.168.1.1
Output
✓ Match
Valid IP
Input
255.255.255.255
Output
✓ Match
Valid IP
Input
0.0.0.0
Output
✓ Match
Invalid - octet > 255
Input
256.1.1.1
Output
✗ No match
Invalid - missing octet
Input
192.168.1
Output
✗ No match

Code Examples

JavaScript 
const ipv4Regex = /^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/;

const isValidIPv4 = ipv4Regex.test('192.168.1.1'); // true
Python 
import ipaddress

# Better to use built-in library
try:
    ip = ipaddress.IPv4Address('192.168.1.1')
    print(f'Valid IP: {ip}')
except ipaddress.AddressValueError:
    print('Invalid IP')

Try it Now

Open in Regex Tester

💡 Tips

  • Use built-in IP address libraries when possible
  • Check for reserved ranges (127.0.0.0/8, 10.0.0.0/8, etc.)
  • Consider if you need to support CIDR notation
  • Validate each octet is truly 0-255

⚠️ Common Pitfalls

  • Leading zeros may be interpreted as octal in some contexts
  • Does not validate if IP is routable or reserved
  • Does not check CIDR notation
  • Consider using IP address libraries for production
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