REGEXVAULTv2.0
Web & Network/IPv6
Verified Safe

IPv6 with CIDR Prefix Length Regex for Go

/^[0-9a-fA-F:]+\/(?:12[0-8]|1[01][0-9]|[1-9][0-9]|[0-9])$/i

What this pattern does

This page provides a well-structured, multi-part regular expression for matching ipv6 with cidr prefix length, ported and verified for Go. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.

Go Implementation

Go
// IPv6 with CIDR Prefix Length
// ReDoS-safe | RegexVault — Web & Network > IPv6

package validation

import "regexp"

var ipv6WithCidrPrefixLengthRe = regexp.MustCompile(`^[0-9a-fA-F:]+\/(?:12[0-8]|1[01][0-9]|[1-9][0-9]|[0-9])$`)

func ValidateIpv6WithCidrPrefixLength(s string) bool {
    return ipv6WithCidrPrefixLengthRe.MatchString(s)
}

// Example
// fmt.Println(ValidateIpv6WithCidrPrefixLength("2001:db8::/32")) // true

Test Cases

Matches (Valid)
Rejects (Invalid)
2001:db8::/322001:db8::/129
fe80::/102001:db8::/-1
::1/1282001:db8::
::/0192.168.0.0/24
2001:db8:85a3::8a2e:0370:7334/642001:db8::/

When to use this pattern

This pattern is drawn from the Web & Network > IPv6 category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

12[0-8] covers 120–128; [01][0-9] would incorrectly cover 100–119 and 000–019, so use 1[01][0-9] for the 100–119 range.

Technical Notes

The IPv6 portion uses a simplified [0-9a-fA-F:]+ to avoid duplicating the full IPv6 validation. Pair with net-ipv6-02 for full address validation before applying this pattern.

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