IPv6

IPv6 Expander

Expand, compress, and inspect IPv6 addresses with RFC 5952 canonical output, prefixes, and zone IDs.

IPv6 Expander

Expand, compress, and inspect IPv6 addresses with RFC 5952 canonical output, prefixes, and zone IDs.

IPv6 address

Accepts :: compression, embedded IPv4, %zone, /prefix, and bracketed forms like [::1]:8080.

Sample addresses

Analysis

Everything is recalculated as you type and nothing leaves your browser.

Fully expanded: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Canonical (RFC 5952): 2001:db8:85a3::8a2e:370:7334
128-bit value (hex): 0x20010db885a3000000008a2e03707334
Reverse DNS (ip6.arpa): 4.3.3.7.0.7.3.0.e.2.a.8.0.0.0.0.0.0.0.0.3.a.5.8.8.b.d.0.1.0.0.2.ip6.arpa
Network address (expanded): 2001:0db8:85a3:0000:0000:0000:0000:0000
Network address (canonical): 2001:db8:85a3::

Details

Address type: Documentation
Reserved range: 2001:db8::/32
Prefix length: /64
Addresses in block: 2^64

Groups

#	Hex	Decimal	Binary
1	2001	8193	0010000000000001
2	0db8	3512	0000110110111000
3	85a3	34211	1000010110100011
4	0000	0	0000000000000000
5	0000	0	0000000000000000
6	8a2e	35374	1000101000101110
7	0370	880	0000001101110000
8	7334	29492	0111001100110100

What

IPv6 Expander definition

An IPv6 address can be written fully expanded, shortened with ::, or mixed with a trailing IPv4 part. This tool normalizes any of those forms into the same 128-bit value and shows the RFC 5952 canonical text, the eight groups, the reverse DNS name, and the address type.

Cases

Use Cases

Normalize IPv6 addresses before comparing them in logs or firewall rules.

Turn a shortened address into the expanded form a config file expects.

Build the ip6.arpa name needed for a reverse DNS (PTR) record.

Check whether an address is link-local, unique local, multicast, or global.

Verify the network address and size of a prefix such as /48 or /64.

Pull the IPv4 hidden inside ::ffff: mapped or 6to4 addresses.

How To

How to expand an IPv6 address

Paste any IPv6 form and read every representation side by side.

Paste an address

Enter an IPv6 address in any notation, with an optional %zone or /prefix.

Compare the forms

Contrast the fully expanded form with the RFC 5952 canonical short form.

Inspect the details

Check the address type, group table, reverse DNS name, and prefix maths.

Copy what you need

Use the copy button on any row to paste it into a config file or ticket.

Knowledge

Understanding IPv6 notation

The eight groups

An IPv6 address is 128 bits written as eight groups of four hex digits. Leading zeros in a group may be dropped, and one run of all-zero groups may be replaced with ::.

Prefixes and scopes

The /prefix marks how many leading bits identify the network, so a /64 leaves 2^64 addresses for hosts. Those leading bits also set the scope: fe80::/10 is link-local, fc00::/7 is unique local, and ff00::/8 is multicast.

Parsing pitfalls

Comparing addresses as raw text is unsafe because one address has many spellings, so always normalize to the expanded form or the 128-bit value first. Also reject IPv4 tails with leading zeros such as ::ffff:010.0.0.1, since octal-looking octets are a classic allowlist bypass.

FAQ

What does expanding an IPv6 address mean?

It writes all eight groups with four hex digits and removes the :: shorthand, so 2001:db8::1 becomes 2001:0db8:0000:0000:0000:0000:0000:0001.

What makes a compressed form canonical?

RFC 5952 requires lowercase hex, no leading zeros, and :: applied to the single longest run of zero groups, picking the leftmost run on a tie.

Why can :: appear only once?

Each :: stands for an unknown number of zero groups, so using two of them would make the address ambiguous.

What is the %eth0 part after some addresses?

That is a zone ID. Link-local addresses repeat on every interface, so the zone tells the OS which interface to use.

How do I build a reverse DNS name for IPv6?

Expand the address, reverse its 32 hex nibbles, separate them with dots, and append ip6.arpa. The tool does this for you.

Is my address sent anywhere?

No. Parsing and formatting run entirely in your browser, with no network requests.

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IPv6

IPv6 Expander

Expand, compress, and inspect IPv6 addresses with RFC 5952 canonical output, prefixes, and zone IDs.

IPv6 Expander

Expand, compress, and inspect IPv6 addresses with RFC 5952 canonical output, prefixes, and zone IDs.

IPv6 address

Accepts :: compression, embedded IPv4, %zone, /prefix, and bracketed forms like [::1]:8080.

Sample addresses

Analysis

Everything is recalculated as you type and nothing leaves your browser.

Fully expanded: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Canonical (RFC 5952): 2001:db8:85a3::8a2e:370:7334
128-bit value (hex): 0x20010db885a3000000008a2e03707334
Reverse DNS (ip6.arpa): 4.3.3.7.0.7.3.0.e.2.a.8.0.0.0.0.0.0.0.0.3.a.5.8.8.b.d.0.1.0.0.2.ip6.arpa
Network address (expanded): 2001:0db8:85a3:0000:0000:0000:0000:0000
Network address (canonical): 2001:db8:85a3::

Details

Address type: Documentation
Reserved range: 2001:db8::/32
Prefix length: /64
Addresses in block: 2^64

Groups

#	Hex	Decimal	Binary
1	2001	8193	0010000000000001
2	0db8	3512	0000110110111000
3	85a3	34211	1000010110100011
4	0000	0	0000000000000000
5	0000	0	0000000000000000
6	8a2e	35374	1000101000101110
7	0370	880	0000001101110000
8	7334	29492	0111001100110100

What

IPv6 Expander definition

Cases

Use Cases

Normalize IPv6 addresses before comparing them in logs or firewall rules.

Turn a shortened address into the expanded form a config file expects.

Build the ip6.arpa name needed for a reverse DNS (PTR) record.

Check whether an address is link-local, unique local, multicast, or global.

Verify the network address and size of a prefix such as /48 or /64.

Pull the IPv4 hidden inside ::ffff: mapped or 6to4 addresses.

How To

How to expand an IPv6 address

Paste any IPv6 form and read every representation side by side.

Paste an address

Enter an IPv6 address in any notation, with an optional %zone or /prefix.

Compare the forms

Contrast the fully expanded form with the RFC 5952 canonical short form.

Inspect the details

Check the address type, group table, reverse DNS name, and prefix maths.

Copy what you need

Use the copy button on any row to paste it into a config file or ticket.

Knowledge

Understanding IPv6 notation

The eight groups

An IPv6 address is 128 bits written as eight groups of four hex digits. Leading zeros in a group may be dropped, and one run of all-zero groups may be replaced with ::.

Prefixes and scopes

Parsing pitfalls

FAQ

What does expanding an IPv6 address mean?

It writes all eight groups with four hex digits and removes the :: shorthand, so 2001:db8::1 becomes 2001:0db8:0000:0000:0000:0000:0000:0001.

What makes a compressed form canonical?

RFC 5952 requires lowercase hex, no leading zeros, and :: applied to the single longest run of zero groups, picking the leftmost run on a tie.

Why can :: appear only once?

Each :: stands for an unknown number of zero groups, so using two of them would make the address ambiguous.

What is the %eth0 part after some addresses?

That is a zone ID. Link-local addresses repeat on every interface, so the zone tells the OS which interface to use.

How do I build a reverse DNS name for IPv6?

Expand the address, reverse its 32 hex nibbles, separate them with dots, and append ip6.arpa. The tool does this for you.

Is my address sent anywhere?

No. Parsing and formatting run entirely in your browser, with no network requests.