IPv6 Host Range Calculator
Show the first and last address inside an IPv6 prefix along with the size of the address space it covers.
About IPv6 Host Range Calculator
Clearing every host bit gives the first address; setting them all gives the last. Because IPv6 has no broadcast address, both ends of the range are usable, although the all-zeros address is reserved as the subnet-router anycast address. Explicit bounds are what you paste into firewall objects and DDoS scrubbing policies, and they make it obvious when two prefixes overlap.
Formula
IPv6 Host Range
first = address AND mask, last = first OR NOT(mask), count = 2^(128 − prefix).
- p
- Prefix length in bits
- mask
- Prefix mask applied per 16-bit group
Worked example
With the default values below, IPv6 Host Range Calculator returns First Address of 2001:db8:acad:1::. Change any input above and every figure here is recalculated in your browser.
Inputs used
- IPv6 address
- 2001:db8:acad:1::
- Prefix lengthaccepts 0–128 bits
- 64 bits
Results
- First Address
- 2001:db8:acad:1::
- Last Address
- 2001:0db8:acad:0001:ffff:ffff:ffff:ffff
- Addresses in Prefix
- 18,446,744,073,709,552,000
- Equivalent /64 Subnets
- 1
Step by step
- 1Values used
- 2IPv6 Host Range
- 3First Address= 2001:db8:acad:1::
- 4Last Address= 2001:0db8:acad:0001:ffff:ffff:ffff:ffff
- 5Addresses in Prefix= 18,446,744,073,709,552,000
- 6Equivalent /64 Subnets= 1
Assumptions and limits
- The result is derived only from the 2 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
How is IPv6 Host Range calculated?
first = address AND mask, last = first OR NOT(mask), count = 2^(128 − prefix). Clearing every host bit gives the first address; setting them all gives the last. Because IPv6 has no broadcast address, both ends of the range are usable, although the all-zeros address is reserved as the subnet-router anycast address.
Why does IPv6 Host Range matter?
Explicit bounds are what you paste into firewall objects and DDoS scrubbing policies, and they make it obvious when two prefixes overlap.
What values do I need to enter?
This calculator takes 2 inputs: IPv6 address, Prefix length. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.