IPv6 subnet calculator

IPv6 subnetting works like IPv4 but at a much larger scale. Instead of counting individual hosts, you usually plan how many /64 networks fit inside the prefix your ISP or cloud provider gives you. This calculator shows the network address, address range and size for any IPv6 CIDR prefix.

How to use it

1. Enter an IPv6 address with a prefix length, for example 2001:db8:abcd::/48.
2. Read the network address, first and last addresses and total address count.

Example: 2001:db8:abcd::/48

• Network: 2001:db8:abcd::
• Last address: 2001:db8:abcd:ffff:ffff:ffff:ffff:ffff
• Total addresses: 2^80
• Number of /64 subnets: 2^16 = 65,536

Common IPv6 prefix sizes

• /32: typical allocation to an ISP or large organisation.
• /48: common allocation to a business site; 65,536 subnets.
• /56: common for home broadband; 256 subnets.
• /64: the standard size of a single LAN. It contains 18,446,744,073,709,551,616 addresses.
• /128: a single address, used for loopbacks and host routes.

Why every LAN should be a /64

SLAAC, the mechanism devices use to configure their own addresses, requires a 64-bit interface identifier. Using a longer prefix like /80 on a LAN breaks SLAAC and some other features. Point-to-point router links may use /127.

Planning tip

Subnet on nibble boundaries (multiples of 4 bits, such as /48, /52, /56, /60, /64). Each hex digit then corresponds to a level of your addressing plan, which keeps addresses readable and makes reverse DNS delegation simple.