IPv6 Subnet Calculator
The IPv6 subnet calculator takes any IPv6 address and prefix length (for example 2001:db8::/48) and returns the network address in compressed and expanded form, the total number of addresses, and the /64 subnets the block contains.
IPv6 planning is about subnets, not hosts. SLAAC requires every LAN to be a /64, so the practical question is always how a larger allocation breaks into /64s: a /48 - the standard allocation for a site - contains 65,536 /64 subnets, and the calculator shows the first and last of them.
IPv6 Subnet Calculator
Find the network address, expanded form, /64 subnet count, and first/last /64 for any IPv6 prefix.
Enter values above to see results.
Frequently Asked Questions
How many /64 subnets are in a /48?
A /48 contains 65,536 /64 subnets (2 raised to the power of 64 minus 48). Each /64 can be assigned to a single LAN segment for SLAAC.
Why is /64 the standard subnet size in IPv6?
SLAAC stateless address autoconfiguration requires a /64 so hosts can derive their address from the router advertisement. Assigning anything smaller breaks SLAAC, so /64 has become the universal unit of IPv6 subnetting.
How do I break a /48 into /64 subnets?
Increment the third hextet of the /48. For 2001:db8::/48 the subnets are 2001:db8:0::/64, 2001:db8:1::/64, 2001:db8:2::/64, and so on up to 2001:db8:ffff::/64.
Read More
Guides that go deeper on the same topic.
IPv6 Address Management: A Practical Guide to Subnetting, Planning, and Dual-Stack Migration
A practical guide to IPv6 address management: /64 subnetting, /48 site planning, ULA, dual stack migration, and pitfalls that catch teams moving from IPv4.
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