# IPv6 range to cidrs

`ipv6-range-to-cidrs` · version 1.0.0 · URLs & IP addresses · free, no key needed

Convert an arbitrary IPv6 address range into the minimal list of CIDR blocks that exactly covers it.

**Use when you need to: ipv6 range to cidr · convert ipv6 range to cidrs · summarize ipv6 address range.**

## Supported

- ipv6 range to cidr
- convert ipv6 range to cidrs
- summarize ipv6 address range

## Not supported

- IPv4
- hyphenated single-string ranges

## Behavior

- first_address and last_address accept any RFC 4291 textual form (see ipv6-parse); first_address must not exceed last_address as a 128-bit value.
- cidrs is the minimal ordered list of non-overlapping CIDR blocks (largest-first at each step) whose union is exactly [first_address, last_address].
- A single address (first_address equal to last_address) yields one /128 block.

## Input

- `first_address` (string, required): max length 45
- `last_address` (string, required): max length 45

## Output

- `cidrs` (array of string, required): max items 256; each max length 49
- `count` (integer, required): min 1; max 256

## Limits

- max address length: 45
- max output blocks: 256

## Example

Request input:

```json
{
  "first_address": "2001:db8::9",
  "last_address": "2001:db8::b"
}
```

Response:

```json
{
  "result": {
    "cidrs": [
      "2001:db8::9/128",
      "2001:db8::a/127"
    ],
    "count": 2
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "ipv6-range-to-cidrs",
  "version": "1.0.0",
  "input": {
    "first_address": "2001:db8::9",
    "last_address": "2001:db8::b"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/ipv6-range-to-cidrs/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"first_address":"2001:db8::9","last_address":"2001:db8::b"}'
```

The machine-readable contract is at [/v1/tools/ipv6-range-to-cidrs/versions/1.0.0](/v1/tools/ipv6-range-to-cidrs/versions/1.0.0).

### CLI

```sh
node cli.mjs run ipv6-range-to-cidrs 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [IPv4 range to cidrs](/tools/ipv4-range-to-cidrs): Convert an arbitrary IPv4 address range into the minimal list of CIDR blocks that exactly covers it.
- [IPv6 address offset](/tools/ipv6-address-offset): Add a signed integer offset to an IPv6 address, throwing if the result leaves the IPv6 address space.
- [IPv6 CIDR aggregate](/tools/ipv6-cidr-aggregate): Merge a list of IPv6 CIDR blocks into the minimal equivalent list of non-overlapping CIDR blocks.
- [IPv6 CIDR parse](/tools/ipv6-cidr-parse): Parse an IPv6 CIDR block into its canonical network address, prefix, first/last address, and total address count.
- [IPv6 in CIDR](/tools/ipv6-in-cidr): Test whether an IPv6 address lies in a CIDR prefix whose host bits are zero.
- [IPv6 parse](/tools/ipv6-parse): Parse an IPv6 address (any RFC 4291 textual form) into its 8 hextets and a 128-bit integer string.