IPv6 Site Prefix Capacity Calculator

Method, formula and assumptions

Each extra prefix bit doubles the number of equal subdivisions. Site count = 2^(site - delegated prefix), LAN count per site = 2^(LAN - site). Subtract planned sites without hiding over-allocation.

Input definitions and supported units

• Delegated prefix length: Whole-number count, from 16 to 64; must be positive.
• Site prefix length: Whole-number count, from 16 to 64; must be positive.
• LAN prefix length: Whole-number count, from 16 to 64; must be positive.
• Sites to allocate: Whole-number count, from 0 to 1000000; zero is supported where the stated method permits it.

Worked example with answer

A /48 divided into /56 sites yields 256 sites, each with 256 /64 LANs. Allocating 200 sites leaves 56, with 65,536 LAN prefixes across the original block.

How to use the results

Negative remaining prefixes means the allocation exceeds the block. All calculations count prefixes, not individual IPv6 addresses.

Results retain full precision internally and display up to four decimal places. Very small nonzero results use scientific notation rather than appearing as zero. Check the labels before comparing values across units.

Limitations and references

Does not assert what a provider delegates or what a host accepts. Equal subdivision does not account for reserved sites, hierarchy policy or route aggregation choices.

The method is a self-contained arithmetic, geometric or explicitly stated mathematical model. There are no imported tariffs, empirical presets or equipment specifications; measured values and allowances must come from your own process.

Related planning tools

• IPv4 Equal-Subnet Host Planner
• Rack Unit Allocation Planner

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