Dual Stack Addressing Plan Calculator

Work out dual stack addressing plan instantly with clear inputs, formula shown and shareable results.

About Dual Stack Addressing Plan Calculator

A dual-stack plan numbers both families on the same topology. IPv4 needs a bit budget: sites multiplied by subnets per site rounded up to a power of two tells you how many subnet bits to reserve. IPv6 is allocated by prefix instead of by host count — a /48 per site yields 65,536 /64 links — and the site prefixes then aggregate into one shorter prefix for the whole estate.

Formula

Dual-stack budget

IPv4 subnets = sites x subnets per site; subnet bits = ceil(log2(subnets)); IPv6 /64s per site = 2^(64 - site prefix); aggregate = site prefix - ceil(log2(sites))

Worked example

With the default values below, Dual Stack Addressing Plan Calculator returns IPv4 subnets in the plan of 96. Change any input above and every figure here is recalculated in your browser.

Inputs used

Number of sitesminimum 1: 12
IPv4 subnets per siteminimum 1: 8
IPv6 prefix per site (/n)accepts 32–64 bits: 48 bits

Results

IPv4 subnets in the plan: 96
Bits needed to number all IPv4 subnets: 7 bits
IPv6 /64s available per site: 65,536
IPv6 aggregate covering every site: 44 /n

Step by step

1Values used
2Dual-stack budget
3IPv4 subnets in the plan= 96
4Bits needed to number all IPv4 subnets= 7 bits
5IPv6 /64s available per site= 65,536
6IPv6 aggregate covering every site= 44 /n

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why always a /64 per link?

SLAAC and many IPv6 features assume 64 host bits. Using a longer prefix on a LAN breaks autoconfiguration, so subnet on nibble boundaries above /64 instead.

Should IPv4 and IPv6 subnet numbers line up?

Encoding the VLAN ID into the IPv6 subnet field, for example 2001:db8:1:20::/64 for VLAN 20, makes troubleshooting far easier than unrelated numbering.