Compressed and expanded forms
The same address written two ways. The compressed form follows RFC 5952: lowercase, no leading zeros, and :: in place of the longest run of zero groups. The expanded form writes all eight groups in full.
IPv6 subnet calculator
Find the range an IPv6 prefix covers and how many /64s it holds, then split it into the prefixes you hand to your customers. It runs in your browser: nothing you type is sent anywhere.
- Network
- 2001:db8::/48
- Compressed
- 2001:db8::
- Expanded
- 2001:0db8:0000:0000:0000:0000:0000:0000
- First address
- 2001:db8::
- Last address
- 2001:db8:0:ffff:ffff:ffff:ffff:ffff
- /64 subnets
- 65,536
What each figure means
How an IPv6 prefix is written, and the sizes ISPs hand out.
First and last address
IPv6 has no broadcast address, so the range runs from the network address to the last one in the prefix.
Why /64s are counted
Each LAN needs a whole /64 for SLAAC to work, so the number of /64s is how many networks a customer can run behind one prefix.
Prefixes for customers
ISPs commonly delegate a /48 or a /56 to each customer over DHCPv6-PD, and a /64 to each point-to-point link. Split your allocation to see the prefixes you can hand out.
IPv4 has its own calculator
For netmasks, broadcast addresses and usable hosts in an IPv4 block, use the subnet calculator.