IPv6 Expand and Compress (RFC 5952)

Expand, compress and validate IPv6 addresses and prefixes.

IPv6 addresses

Use via API

Validate an IPv6 address and return its expanded and compressed forms, address type, reverse DNS name, embedded IPv4, integer value and, with a prefix, the network range. Send JSON, get JSON back.

POST https://pithlab.com/api/v1/tools/ipv6-address-tool

curl https://pithlab.com/api/v1/tools/ipv6-address-tool \
  -H "Authorization: Bearer $PITHLAB_KEY" \
  -H "Content-Type: application/json" \
  -d '{"address":"2001:db8:0:0:8:800:200c:417a/64"}'

Fields and response OpenAPI document Get an API key

About the IPv6 Expand and Compress

Expand or compress IPv6 addresses to RFC 5952 form, validate them, find the address type and prefix range, and get the ip6.arpa reverse DNS name.

How to use the IPv6 Expand and Compress

Paste one IPv6 address per line. You can include a prefix such as /64, a zone ID such as %eth0, or an embedded IPv4 part.
Each line shows the compressed RFC 5952 form, the full expanded form, the address type and the reverse DNS name.
If you add a prefix, the first and last address of that network and its size are shown too.
Copy any single value, or copy all compressed or expanded results at once.

Examples

Compress a full address

Input

2001:0DB8:0000:0000:0000:ff00:0042:8329

Output

Compressed: 2001:db8::ff00:42:8329
Expanded: 2001:0db8:0000:0000:0000:ff00:0042:8329
Type: Documentation (RFC 3849)

A /64 network range

Input

2001:db8:85a3::8a2e:370:7334/64

Output

Compressed: 2001:db8:85a3::8a2e:370:7334/64
Expanded: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
Type: Documentation (RFC 3849)
Network: 2001:db8:85a3::/64
First: 2001:db8:85a3::
Last: 2001:db8:85a3:0:ffff:ffff:ffff:ffff
Addresses: 18,446,744,073,709,551,616

IPv4-mapped address

Input

::ffff:192.0.2.1

Output

Compressed: ::ffff:192.0.2.1
Expanded: 0000:0000:0000:0000:0000:ffff:c000:0201
Type: IPv4-mapped
IPv4: 192.0.2.1

Link-local with a zone ID

Input

fe80::1%eth0

Output

Compressed: fe80::1%eth0
Expanded: fe80:0000:0000:0000:0000:0000:0000:0001
Type: Link-local unicast
Zone: eth0

Frequently asked questions

What are the RFC 5952 compression rules?

Use lowercase hex, drop leading zeros in each group, and replace the longest run of two or more all-zero groups with ::. If two runs are equally long, the first one is compressed. A single zero group is written as 0, never ::.

Why does 2001:db8:0:0:1:0:0:1 become 2001:db8::1:0:0:1?

There are two runs of two zero groups. RFC 5952 says to compress the leftmost when runs tie, so the first pair becomes :: and the second stays as 0:0.

What is a zone ID?

Link-local addresses such as fe80::1 exist on every interface, so a zone ID like %eth0 or %3 says which interface is meant. It is kept in the compressed output but is not part of the address bits.

How is the reverse DNS name built?

The address is expanded to 32 hex digits, the digits are reversed, separated by dots and followed by ip6.arpa. That is the name a PTR record for the address lives under.

Which address types are recognised?

Unspecified, loopback, IPv4-mapped, NAT64, discard-only, documentation (2001:db8::/32 and 3fff::/20), Teredo, 6to4, unique local (fc00::/7), link-local, deprecated site-local, multicast with its scope, and global unicast.