IPv6 CIDR subnets

ipv6-cidr-subnets · version 1.0.0 · URLs & IP addresses · free, no key needed

Split an IPv6 CIDR block into the full ordered list of equal-size subnets at a given longer prefix.

Use when you need to: ipv6 cidr subnets · split ipv6 cidr into subnets · ipv6 subnetting.

Supported

• ipv6 cidr subnets
• split ipv6 cidr into subnets
• ipv6 subnetting

Not supported

• IPv4
• unequal (VLSM) splits
• splitting into a target subnet count instead of a prefix

Behavior

• cidr is address/prefix with host bits zero; new_prefix is a JSON integer strictly greater than cidr's prefix and at most 128.
• subnets is the ordered list of all 2^(new_prefix - prefix) equal-size /new_prefix blocks that exactly partition cidr, network-address first.
• Throws if 2^(new_prefix - prefix) would exceed 4096.

Input

• cidr (string, required): max length 49
• new_prefix (integer, required): min 0; max 128

Output

• subnets (array of string, required): max items 4096; each max length 49
• count (integer, required): min 1; max 4096

Limits

• max cidr length: 49
• prefix max: 128
• max output subnets: 4096

Example

Request input:

{
  "cidr": "2001:db8::/32",
  "new_prefix": 34
}

Response:

{
  "result": {
    "subnets": [
      "2001:db8::/34",
      "2001:db8:4000::/34",
      "2001:db8:8000::/34",
      "2001:db8:c000::/34"
    ],
    "count": 4
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "ipv6-cidr-subnets",
  "version": "1.0.0",
  "input": {
    "cidr": "2001:db8::/32",
    "new_prefix": 34
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/ipv6-cidr-subnets/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"cidr":"2001:db8::/32","new_prefix":34}'

The machine-readable contract is at /v1/tools/ipv6-cidr-subnets/versions/1.0.0.

CLI

node cli.mjs run ipv6-cidr-subnets 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• IPv4 CIDR subnets: Split an IPv4 CIDR block into the full ordered list of equal-size subnets at a given longer prefix.
• IPv6 CIDR aggregate: Merge a list of IPv6 CIDR blocks into the minimal equivalent list of non-overlapping CIDR blocks.
• IPv4 CIDR aggregate: Merge a list of IPv4 CIDR blocks into the minimal equivalent list of non-overlapping CIDR blocks.
• IPv6 CIDR contains: Test whether one IPv6 CIDR block fully contains another IPv6 CIDR block.
• IPv6 CIDR overlap: Test whether two IPv6 CIDR blocks overlap (share at least one address).
• IPv6 CIDR parse: Parse an IPv6 CIDR block into its canonical network address, prefix, first/last address, and total address count.