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IPv6 Address Validation Regex

• CronOS Team
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IPv6 Address Validation Regex

Validate IPv6 addresses in standard format with 8 groups of 1-4 hexadecimal digits separated by colons.

Pattern Breakdown

regex
^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}$

Components

ComponentDescriptionMatches
^Start anchorEnsures match from string start
([0-9a-fA-F]{1,4}:){7}First 7 groupsExactly 7 groups of 1-4 hex digits + colon
[0-9a-fA-F]{1,4}Final groupLast group of 1-4 hex digits (no trailing colon)
$End anchorEnsures match to string end

Character Classes

  • [0-9a-fA-F] - Hexadecimal digits: 0-9, a-f, A-F
  • {1,4} - Quantifier: between 1 and 4 occurrences
  • {7} - Quantifier: exactly 7 occurrences
  • : - Literal colon separator

Examples

Valid:

  • 2001:0db8:85a3:0000:0000:8a2e:0370:7334
  • 2001:db8:85a3:0:0:8a2e:370:7334 (compressed zeros)
  • 2001:db8:85a3::8a2e:370:7334 (double colon compression - not supported by this pattern)
  • ::1 (localhost - not supported by this pattern)
  • fe80::1 (compressed - not supported by this pattern)

Invalid:

  • 2001:0db8:85a3:0000:0000:8a2e:0370 (only 7 groups)
  • 2001:0db8:85a3:0000:0000:8a2e:0370:7334:1234 (9 groups)
  • 2001:0db8:85a3:0000:0000:8a2e:0370:733g (invalid hex character)
  • 2001:0db8:85a3:0000:0000:8a2e:0370:73345 (group too long, 5 digits)
  • 2001::db8:85a3:0000:0000:8a2e:0370:7334 (double colon not supported)

Implementation

JavaScript

javascript
const ipv6Regex = /^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}$/;
ipv6Regex.test('2001:0db8:85a3:0000:0000:8a2e:0370:7334'); // true
ipv6Regex.test('2001:db8:85a3:0:0:8a2e:370:7334'); // true
ipv6Regex.test('2001:0db8:85a3:0000:0000:8a2e:0370'); // false (incomplete)
ipv6Regex.test('2001::db8:85a3:0000:0000:8a2e:0370:7334'); // false (double colon)

Python

python
import re
ipv6_regex = r'^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}$'
bool(re.match(ipv6_regex, '2001:0db8:85a3:0000:0000:8a2e:0370:7334'))  # True
bool(re.match(ipv6_regex, '2001:db8:85a3:0:0:8a2e:370:7334'))  # True
bool(re.match(ipv6_regex, '2001::db8:85a3:0000:0000:8a2e:0370:7334'))  # False (double colon)

Go

go
ipv6Regex := regexp.MustCompile(`^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}$`)
ipv6Regex.MatchString("2001:0db8:85a3:0000:0000:8a2e:0370:7334") // true
ipv6Regex.MatchString("2001:db8:85a3:0:0:8a2e:370:7334") // true
ipv6Regex.MatchString("2001::db8:85a3:0000:0000:8a2e:0370:7334") // false (double colon)

Limitations

  1. No zero compression: Doesn't support :: (double colon) for compressed zeros
  2. No IPv4-mapped IPv6: Doesn't support ::ffff:192.168.1.1 format
  3. Strict format: Requires all 8 groups explicitly (no compression)
  4. No leading zero compression: Doesn't handle 2001:db8::1 format
  5. Format only: Validates format, not network reachability

When to Use

  • Strict IPv6 format validation
  • When you need uncompressed IPv6 addresses
  • Network configuration that requires explicit format
  • When zero compression is not allowed
  • Basic IPv6 format checking

For production, consider:

  • Supporting zero compression (::) for more flexible validation
  • Supporting IPv4-mapped IPv6 addresses
  • Using IPv6 parsing libraries for comprehensive validation
  • Handling mixed IPv4/IPv6 formats
  • Validating against reserved IPv6 ranges if needed

Need to generate a regex pattern?

Use CronOS to generate any regex pattern you wish with natural language. Simply describe what you need, and we'll create the perfect regex pattern for you. It's completely free!

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