128-bit BigInt engine

IPv6 subnet calculator.

Calculate IPv6 prefix networks, address capacities, RFC 5952 canonical compression and reverse DNS delegations.

IPv6 Address & Prefix

Accepts compressed (e.g. 2001:db8::1) or expanded formats

Prefix Length: /64Host Bits: 64

Quick Presets:

IPv6 Scope

Documentation (RFC 3849)

Prefix: /64

Total IP Addresses

18,446,744,073,709,551,616

2^64 addresses

Possible /64 Subnets

Standard SLAAC blocks

IPv6 Representation & Ranges

Canonical Compressed (RFC 5952)

2001:db8:abcd:12::1

Full Expanded Form (128 bits)

2001:0db8:abcd:0012:0000:0000:0000:0001

Subnet Range Start

2001:db8:abcd:12::

Subnet Range End

2001:db8:abcd:12:ffff:ffff:ffff:ffff

Reverse DNS Zone (.ip6.arpa)

1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.1.0.0.d.c.b.a.8.b.d.0.1.0.0.2.ip6.arpa

IP subnet calculator for IPv6

IPv6 addresses are 128 bits long, written as eight groups of hexadecimal digits. Subnetting works exactly like IPv4 — a prefix length says how many leading bits identify the network — but the numbers are enormous, so this IPv6 subnet calculator uses exact 128-bit integer arithmetic rather than floating-point estimates.

IPv6 CIDR and prefix lengths

Prefix	Typical use	/64 subnets
/32	ISP allocation	4,294,967,296
/48	Site / organisation	65,536
/56	Home or small site	256
/64	Single LAN (SLAAC)	1
/127	Router point-to-point link	n/a

See the IPv6 prefix length guide for the full reference and address types.

Compressing and expanding IPv6 addresses

Enter any valid form — compressed (2001:db8::1), expanded or with an embedded IPv4 tail (::ffff:192.0.2.1) — and the calculator shows both the expanded and RFC 5952 canonical representation, the reverse DNS ip6.arpa name and the address type (global unicast, unique local, link-local, multicast and more).

IPv4 or IPv6?

Working with legacy networks? Use the IPv4 subnet calculator, or the CIDR calculator for notation conversions that apply to both families.

Frequently asked questions

What is an IPv6 subnet calculator?

An IPv6 subnet calculator takes an IPv6 address and prefix length and shows the network prefix, first and last address of the range, number of addresses, number of /64 subnets and the compressed and expanded forms of the address.

What prefix length should an IPv6 LAN use?

Always /64. SLAAC and many IPv6 features require a 64-bit interface identifier. Point-to-point router links commonly use /127 (RFC 6164).

How many addresses are in a /64?

2^64 = 18,446,744,073,709,551,616 addresses — more than the entire IPv4 Internet squared.

How do I shorten an IPv6 address?

Remove leading zeros in each group and replace the longest run of all-zero groups with "::" (once only). RFC 5952 defines the canonical form: 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1.

Can I use VLSM with IPv6?

The idea applies, but because address space is vast you normally use /64 for every subnet and plan the upper bits (e.g. /48 per site, /56 per building) hierarchically.