IPv6 Calculator¶

Input¶

Enter an IPv6 address with a prefix length (e.g. 2001:db8::/32 or fe80::1/64). Both full and compressed forms are accepted.

Result rows¶

Row	Description
Network (CIDR)	Network address + prefix
Prefix Length	e.g. `/32`
First IP	First address in the block
Last IP	Last address in the block
Total Addresses	Count (or `2^N` for very large blocks)
Address Type	Global Unicast / Link-local / Multicast / ULA / Loopback / …
Address (Expanded)	Full 128-bit form with all leading zeros
Address (Compressed)	RFC 5952 canonical compressed form
Reverse DNS Zone	`ip6.arpa` zone

Binary / Hex Representation¶

Expand the Binary / Hex Representation panel to see the address in binary (teal = network bits, grey = interface bits) and hexadecimal.

Subnet Splitter¶

Works identically to the IPv4 splitter. For very large splits (prefix difference ≥ 63) the total count is displayed as 2^N.

Overlap Checker¶

The Subnet Overlap Checker is in the Tool Drawer — click the toolbar button on the IPv6 tab. Mixed IPv4/IPv6 pairs are not supported — the checker returns an error ("Cannot compare IPv4 and IPv6 addresses."). See Overlap Checker.

ULA Prefix Generator¶

See IPv6 ULA Generator.

Range → CIDR (v3.3.0)¶

The IPv6 Range → CIDR tool lives in the IPv6 tab's Tool Drawer under the Range→CIDR button. Enter any two IPv6 addresses and it returns the minimal set of CIDR blocks that exactly covers the range, using the greedy largest-aligned-block algorithm.

Internally the tool uses the GMP extension end-to-end, so /128-wide ranges work without overflow. The total_addresses field is returned as a string 2^N whenever the count exceeds PHP_INT_MAX, matching the convention used elsewhere for very large IPv6 sizings.

Output cap. The result is capped at 256 CIDR blocks by default. Pathological fragmented ranges that would otherwise produce thousands of blocks return the first 256 with truncated: true and a yellow warning band on the result; the cap is configurable via $range_max_cidrs in config.php. The same cap applies to the v4 Range → CIDR tool starting in v3.3.0.

Example¶

Input	Output
Start `2001:db8::` · End `2001:db8::ffff`	`2001:db8::/112` (1 block, 65 536 addresses)
Start `2001:db8::1` · End `2001:db8::3`	`2001:db8::1/128`, `2001:db8::2/127` (2 blocks)

REST API¶

curl -sX POST https://example.org/api/v1/range6 \
  -H 'Content-Type: application/json' \
  -d '{"start":"2001:db8::","end":"2001:db8::ffff"}'

Response shape:

{
  "ok": true,
  "data": {
    "cidrs": ["2001:db8::/112"],
    "count": 1,
    "total_addresses": 65536,
    "truncated": false,
    "cap": 256
  }
}

Shareable URL¶

/ipv6/range6?range6_start=2001:db8::&range6_end=2001:db8::ffff

Supernet & Summarise (v3.3.0)¶

The IPv6 Supernet tool lives in the IPv6 tab's Tool Drawer under the Supernet button. It mirrors the v4 Supernet tool and offers two actions on a list of IPv6 CIDRs (one per line, up to 50):

Find — returns the smallest single prefix that fully encloses every input CIDR.
Summarise — merges adjacent and removes contained prefixes, returning the minimal equivalent list in canonical lowercase compressed form.

GMP is used end-to-end so /128-wide inputs and very large counts are handled without overflow.

Examples¶

Action	Input	Output
`find`	`2001:db8::/64`, `2001:db8:0:1::/64`	`2001:db8::/63`
`summarise`	`2001:db8::/65`, `2001:db8:0:0:8000::/65`, `2001:db8::/64`	`2001:db8::/64`

REST API¶

curl -sX POST https://example.org/api/v1/supernet6 \
  -H 'Content-Type: application/json' \
  -d '{"action":"find","cidrs":["2001:db8::/64","2001:db8:0:1::/64"]}'

curl -sX POST https://example.org/api/v1/supernet6 \
  -H 'Content-Type: application/json' \
  -d '{"action":"summarise","cidrs":["2001:db8::/65","2001:db8:0:0:8000::/65"]}'

Shareable URL¶

/ipv6/supernet6?supernet6_action=find&supernet6_input=2001:db8::/64%0A2001:db8:0:1::/64

REST API¶

IPv6 subnet calculations are available programmatically via POST /api/v1/ipv6. The Range → CIDR tool exposes POST /api/v1/range6. The Supernet tool exposes POST /api/v1/supernet6.