IPv4 prefix for hosts

ipv4-prefix-for-hosts · version 1.0.0 · URLs & IP addresses · free, no key needed

Compute the smallest IPv4 CIDR block (largest prefix length) whose usable host capacity meets a required count.

Use when you need to: ipv4 prefix for hosts · subnet size for host count · minimal ipv4 prefix for hosts.

Supported

• ipv4 prefix for hosts
• subnet size for host count
• minimal ipv4 prefix for hosts

Not supported

• IPv6
• VLSM planning across multiple subnets

Behavior

• usable_hosts is a JSON integer from 0 to 4294967294.
• Usable capacity follows RFC 3021: /32 has 1 usable host, /31 has 2, /0-/30 reserve network+broadcast so usable = 2^(32-prefix) - 2.
• prefix is the largest prefix length (smallest block) whose usable capacity is >= usable_hosts.

Input

• usable_hosts (integer, required): min 0; max 4294967294

Output

• prefix (integer, required): min 0; max 32
• netmask (string, required): max length 15
• usable_host_count (string, required): pattern ^(0|[1-9][0-9]*)$
• total_count (string, required): pattern ^(0|[1-9][0-9]*)$

Limits

• usable hosts min: 0
• usable hosts max: 4294967294

Example

Request input:

{
  "usable_hosts": 60
}

Response:

{
  "result": {
    "prefix": 26,
    "netmask": "255.255.255.192",
    "usable_host_count": "62",
    "total_count": "64"
  }
}

How to call it

MCP

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

{
  "id": "ipv4-prefix-for-hosts",
  "version": "1.0.0",
  "input": {
    "usable_hosts": 60
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/ipv4-prefix-for-hosts/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"usable_hosts":60}'

The machine-readable contract is at /v1/tools/ipv4-prefix-for-hosts/versions/1.0.0.

CLI

node cli.mjs run ipv4-prefix-for-hosts 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• IPv4 mask convert: Convert between an IPv4 prefix length, dotted subnet netmask, and dotted wildcard (host) mask.
• IPv4 CIDR contains: Test whether one IPv4 CIDR block fully contains another IPv4 CIDR block.
• IPv4 CIDR overlap: Test whether two IPv4 CIDR blocks overlap (share at least one address).
• IPv4 CIDR parse: Parse an IPv4 CIDR block into its network, broadcast, netmask, wildcard mask, usable host range and address counts.
• IPv4 in CIDR: Test whether a canonical IPv4 address lies in a CIDR prefix whose host bits are zero.
• IPv4 address classify: Classify an IPv4 address against the static IANA IPv4 special-purpose address registry.