# IPv4 CIDR overlap

`ipv4-cidr-overlap` · version 1.0.0 · URLs & IP addresses · free, no key needed

Test whether two IPv4 CIDR blocks overlap (share at least one address).

**Use when you need to: ipv4 cidr overlap · check ipv4 subnet overlap · ipv4 cidr intersects.**

## Supported

- ipv4 cidr overlap
- check ipv4 subnet overlap
- ipv4 cidr intersects

## Not supported

- IPv6

## Behavior

- cidr_a and cidr_b are each dotted-decimal/prefix with host bits zero; otherwise the tool throws.
- overlap is true iff the two blocks share at least one address, including when one fully contains the other or they are identical.

## Input

- `cidr_a` (string, required): max length 18
- `cidr_b` (string, required): max length 18

## Output

- `overlap` (boolean, required)
- `network_a` (string, required): max length 18
- `network_b` (string, required): max length 18

## Limits

- max cidr length: 18

## Example

Request input:

```json
{
  "cidr_a": "10.0.0.0/16",
  "cidr_b": "10.0.128.0/17"
}
```

Response:

```json
{
  "result": {
    "overlap": true,
    "network_a": "10.0.0.0/16",
    "network_b": "10.0.128.0/17"
  }
}
```

## How to call it

### MCP

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

```json
{
  "id": "ipv4-cidr-overlap",
  "version": "1.0.0",
  "input": {
    "cidr_a": "10.0.0.0/16",
    "cidr_b": "10.0.128.0/17"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/ipv4-cidr-overlap/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"cidr_a":"10.0.0.0/16","cidr_b":"10.0.128.0/17"}'
```

The machine-readable contract is at [/v1/tools/ipv4-cidr-overlap/versions/1.0.0](/v1/tools/ipv4-cidr-overlap/versions/1.0.0).

### CLI

```sh
node cli.mjs run ipv4-cidr-overlap 1.0.0 --input input.json --base-url https://computefirst.net
```

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

## Related tools

- [IPv6 CIDR overlap](/tools/ipv6-cidr-overlap): Test whether two IPv6 CIDR blocks overlap (share at least one address).
- [IPv4 CIDR contains](/tools/ipv4-cidr-contains): Test whether one IPv4 CIDR block fully contains another IPv4 CIDR block.
- [IPv4 CIDR parse](/tools/ipv4-cidr-parse): Parse an IPv4 CIDR block into its network, broadcast, netmask, wildcard mask, usable host range and address counts.
- [IPv4 in CIDR](/tools/ipv4-in-cidr): Test whether a canonical IPv4 address lies in a CIDR prefix whose host bits are zero.
- [IPv6 CIDR contains](/tools/ipv6-cidr-contains): Test whether one IPv6 CIDR block fully contains another IPv6 CIDR block.
- [IPv4 CIDR aggregate](/tools/ipv4-cidr-aggregate): Merge a list of IPv4 CIDR blocks into the minimal equivalent list of non-overlapping CIDR blocks.