What does the :: mean in an IPv6 address?

It substitutes one or more consecutive groups of zeros. It may appear at most once per address — otherwise the address is ambiguous. RFC 5952 also says it must replace the longest run of zeros.

Why does my reverse PTR look so long?

ip6.arpa uses one nibble (4 bits) per label, fully reversed. A 128-bit address therefore expands to 32 labels — there's no shortcut.

IPv6 Expander / Compressor

Network

Paste any IPv6 address — compressed (RFC 5952), zero-padded, or anything in between — and see all canonical forms side by side. Useful when debugging firewall rules that demand full notation, generating PTR records for ip6.arpa, or copying a binary representation for documentation.

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IPv6 address

Expanded2001:0db8:0000:0000:0000:8a2e:0370:7334
Compressed2001:db8::8a2e:370:7334
Hex20010db80000000000008a2e03707334
Reverse DNS4.3.3.7.0.7.3.0.e.2.a.8.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa
Binary0010000000000001:0000110110111000:0000000000000000:0000000000000000:0000000000000000:1000101000101110:0000001101110000:0111001100110100

Compression follows RFC 5952 — the longest run of zero groups becomes :: .

How to use

Paste an IPv6 address.
Copy whichever representation you need.

Frequently asked questions

What does the :: mean in an IPv6 address?: It substitutes one or more consecutive groups of zeros. It may appear at most once per address — otherwise the address is ambiguous. RFC 5952 also says it must replace the longest run of zeros.
Why does my reverse PTR look so long?: ip6.arpa uses one nibble (4 bits) per label, fully reversed. A 128-bit address therefore expands to 32 labels — there's no shortcut.

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