By Debmedia Technologies LLP · Kolkata, India · Updated
What Does IPv6 Expand Do?
IPv6 expand turns a shortened IPv6 address into its full form with all eight groups and every leading zero. Short addresses use :: to hide a run of zeros and drop leading zeros inside each group. This tool puts everything back, so 2001:db8::1 becomes 2001:0db8:0000:0000:0000:0000:0000:0001.
The long form is easier to compare, sort and search, and some older software only accepts it.
How to Use IPv6 Expand
- Paste one or more IPv6 addresses, one per line.
- Press Expand.
- Read the full eight-group form for each address.
- Use the third column if you need the ip6.arpa reverse DNS name.
Anatomy of a Full IPv6 Address
| Part | Detail |
|---|---|
| Groups | Eight groups separated by colons |
| Digits per group | Four hexadecimal digits (0 to 9 and a to f) |
| Total size | 128 bits, or 32 hex digits |
| First half | Usually the network prefix |
| Second half | Usually the interface identifier |
The accepted text forms are defined in RFC 4291, which defines the IPv6 text forms.
The Reverse DNS Name
IPv6 reverse DNS writes the 32 hex digits in reverse order, one per label, followed by ip6.arpa. For example, the address 2001:db8::1 has the reverse name 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. The tool prints this name so you can check PTR records with the reverse DNS lookup.
Tips
- Expanded addresses are ideal for log searches, because one address then has one text form.
- Addresses with an IPv4 tail, like ::ffff:192.0.2.33, are converted to pure hex groups.
- Zone IDs such as %eth0 are ignored.
- Up to 200 lines can be expanded at once.
Related Tools
To shorten an address again, use the IPv6 compression tool. To see the range of a prefix, use the CIDR to range converter. If you need to know who owns an address, try the IPv6 WHOIS lookup. All conversions happen in your browser.
When to Expand an Address
Expand an address before you search logs with a plain text search, before you sort a list, and whenever you need to check the exact digits that a double colon hides. It is also the easiest way to learn what an address contains: the first groups show the prefix and the last groups show the device part.
Teachers and students use the expanded form to practise subnetting, because every bit is visible and nothing is implied.
Learn IPv6 by Expanding Addresses
If IPv6 is new to you, try expanding a few well-known addresses: ::1 is the loopback address, fe80:: starts link-local addresses and 2001:db8:: is the documentation range. Seeing every group written out makes the structure obvious, and it helps when you calculate prefixes by hand.
Frequently Asked Questions
Disclaimer: results come from live requests and can change as records and servers change. We cannot guarantee that every answer matches what every visitor sees.