How to use IPv6 Subnet Calculator
Get the best out of IPv6 Subnet Calculator: every option explained, a worked example, and what to check when the output is not what you expected.
Updated July 31, 2026
What it does
Expand, split, and identify host allocations inside IPv6 network address spaces. It runs entirely in your browser — your input never leaves your device.
Options
Every setting this tool exposes, straight from the code that validates it.
| Option | Type | Default | What it does |
|---|---|---|---|
ipv6 | text | 2001:db8::1 | IPv6 address. Defaults to 2001:db8::1. |
prefix | whole number | 64 | Prefix length. Accepts 0–128. Defaults to 64. |
Worked example
Run these settings on the tool page:
ipv6:2001:db8::1prefix:64
You get:
{
"expanded": "2001:0db8:0000:0000:0000:0000:0000:0001",
"compressed": "2001:db8::1",
"prefix": 64,
"networkAddress": "2001:db8::/64",
"firstAddress": "2001:0db8:0000:0000:0000:0000:0000:0000",
"lastAddress": "2001:0db8:0000:0000:ffff:ffff:ffff:ffff",
"addressCount": "2^64"
}
Getting the result you want
Most of the control here is in the options above. If the output is not what you expected, the setting to check first is ipv6 and prefix — those change the shape of the output rather than the input it accepts.
Troubleshooting
- A value is rejected.
prefixaccepts 0–128. Anything outside that is refused rather than silently clamped. - It is slow on very large input. Everything runs in your browser, so speed depends on your device. Very large inputs are best split up, or run through the API where the work happens on our servers.
Automating it
The same logic is available as a REST endpoint, so you can run it from a script, a CI job or your own app.
Bashcurl "https://api.toolsxpo.com/v1/ipv6-subnet" \ -H "Authorization: Bearer $TOOLSXPO_KEY"
It costs 1 credit per successful call. See the full endpoint reference, or try it in the playground.
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