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IPv6 subnetting in short
A /64 is the usual size of one IPv6 subnet, the size of a single LAN. A /48 holds 65,536 of them, a /56 holds 256 and a /32 holds 4,294,967,296. Each /64 has 18,446,744,073,709,551,616 addresses.
The prefix works like it does in IPv4, with 128 bits instead of 32: the number after the slash counts the network bits. For the 32-bit version, see the subnet mask cheat sheet; to find the range of an IPv4 block, use the CIDR calculator.
IPv6 keeps its own private space, the unique local range fc00::/7. For the IPv4 equivalents, see the private IP address ranges.
IPv6 subnet cheat sheet
Four prefix lengths you will meet often, worked out by the same code as the calculator.
| Prefix | Addresses in prefix | Number of /64 subnets |
|---|---|---|
| /32 | 2^96 = 79,228,162,514,264,337,593,543,950,336 | 4,294,967,296 |
| /48 | 2^80 = 1,208,925,819,614,629,174,706,176 | 65,536 |
| /56 | 2^72 = 4,722,366,482,869,645,213,696 | 256 |
| /64 | 2^64 = 18,446,744,073,709,551,616 | 1 |
Compress and expand IPv6 addresses
To compress an address, drop the leading zeros in each group, write the letters in lowercase and replace the longest run of two or more all-zero groups with a double colon, used once. If two runs tie the first one is replaced, and a single zero group is written as 0 (RFC 5952).
So 2001:
IPv6 address types
The Address type row describes the address you typed. The first matching block below is used.
::/128: Unspecified::1/128: Loopback::ffff:0:0/96: IPv4-mappedfe80::/10: Link-localfc00::/7: Unique local (private)ff00::/8: Multicast2001:db8::/32: Documentation2000::/3: Global unicast- Anything else: Other (reserved)
Split a prefix
Pick a longer prefix in Split into to cut the block into equal subnets. The count is 2^(new prefix - prefix), shown exactly. The list shows up to 256 subnets, each with a Copy button, and a note gives the full count when there are more.
2001:db8:abcd::/48 into /50 makes 4 subnets: 2001:db8:abcd::/50, 2001:
Frequently asked questions
How many /64 subnets are in a /48?
A /48 holds 65,536 /64 subnets, because 64 minus 48 is 16 and 2^16 = 65,536. The block 2001:db8:abcd::/48 runs from 2001:db8:abcd:: to 2001:
How do I shorten an IPv6 address?
Drop the leading zeros in each group, then replace the longest run of all-zero groups with a double colon, used once. 2001:
How many addresses are in an IPv6 /64?
An IPv6 /64 has 2^64 = 18,446,744,073,709,551,616 addresses. A single /64 such as 2001:db8:abcd:12::/64 runs from 2001:db8:abcd:12:: to 2001:
Does IPv6 have a broadcast address?
No. IPv6 has no broadcast address; where IPv4 uses broadcast, IPv6 uses multicast. This calculator therefore labels the end of a range "Last address" and never "Broadcast". For 2001:db8:abcd:12::/64 the first address is 2001:db8:abcd:12:: and the last address is 2001:
Why is /64 the usual IPv6 subnet size?
A /64 leaves 64 bits for host addresses, which is the size automatic address setup expects, so /64 is the standard size for a LAN. A site with a /48 can make 65,536 of them. Smaller subnets are possible, but they are usually kept for special cases such as point-to-point links.
What type of address is fe80::1?
fe80::1 is a link-local address. Link-local addresses start with fe80::/10 and work only on the local link, and fe80::1/64 gives the network fe80::/64. The Address type row also names loopback (::1), unique local (fd00::1), multicast (ff02::1), documentation (2001:db8::1) and global unicast (2000::1).