IPv6 Subnet Calculator

Expand any IPv6 prefix to its network range, address count and scope, and enumerate the child subnets a delegation contains.

Calculator IP & Subnetting Runs in your browser
Compressed or expanded notation, with or without a prefix length.
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Result

Prefix
2001:db8:acad::/48
Network (compressed)
2001:db8:acad::
First address
2001:db8:acad::
Last address
2001:db8:acad:ffff:ffff:ffff:ffff:ffff
Addresses in prefix
2^80
/64 subnets available
65,536
Scope
Documentation
2001:db8::/32 - RFC 3849
Prefix length
/48

Details

Expanded network
2001:0db8:acad:0000:0000:0000:0000:0000
Expanded last
2001:0db8:acad:ffff:ffff:ffff:ffff:ffff
Interface ID bits
80
Hex value (network)
0x20010db8acad00000000000000000000

About IPv6 Subnet Calculator

IPv6 subnetting is arithmetic on 128 bits instead of 32, and the numbers stop being intuitive very quickly. This calculator expands a prefix to its first and last address, reports how many child networks it contains, and identifies the RFC scope so you know whether an address is globally routable, link-local or reserved.

Why /64 is the unit of allocation

In IPv6 the subnet is fixed at /64 by convention: the lower 64 bits are the interface identifier used by SLAAC, privacy addressing and EUI-64. You do not conserve addresses by using a /112 - you simply break autoconfiguration for a saving that is meaningless out of 264 addresses.

Allocations work downward from there. A site typically receives a /48 (65,536 subnets) or a /56 (256 subnets) from its provider, and hands each VLAN a /64. Point-to-point links are the one common exception, where /127 is used per RFC 6164.

Compression rules

RFC 5952 defines the canonical text form: lowercase hex, leading zeros in each group removed, and the longest run of consecutive zero groups replaced with :: - once only, and only when it covers two or more groups. This tool always outputs canonical form, which matters when you are diffing configuration or matching log lines.

Common use cases

  • Confirming what a provider-delegated /56 actually contains before carving it into VLAN /64s.
  • Converting between compressed and fully expanded notation for ACLs and log correlation.
  • Checking whether an address is global unicast, ULA, link-local or documentation space.
  • Enumerating the first child prefixes of a delegation to build an addressing plan.

Edge cases and gotchas

  • Prefixes longer than /64 disable SLAAC on that segment.
  • 2001:db8::/32 is documentation space (RFC 3849) - it is not routable, so do not copy examples into production.
  • fe80::/10 link-local addresses are per-link and require a zone index (%eth0) to be unambiguous.

Frequently asked questions

Should I use a /64 or something smaller for a point-to-point link?
Allocate a /64 per link from your plan but configure /127 on the interfaces (RFC 6164). That avoids the neighbour-discovery exhaustion attack surface of a full /64 while keeping the addressing plan uniform.
How many subnets does a /48 contain?
65,536 /64 subnets. A /56 contains 256, and a /60 contains 16.
Is there a broadcast address in IPv6?
No. IPv6 has no broadcast at all - its role is taken by multicast groups such as ff02::1 (all nodes on the link). Every address in a prefix is usable, subject to the anycast subnet-router address convention.