IP in Network Check API: The Complete Guide

Need to check if an IP address falls within a specific network range? This guide covers everything about IP-in-network testing via API, including the matching logic, multiple network checks, and implementation examples.

How Network Matching Works

To check if an IP belongs to a network, we compare the network portion of both addresses. The CIDR prefix length tells us how many bits to compare.

For example, in 192.168.1.0/24, the first 24 bits (192.168.1) must match. So 192.168.1.50 is in the network, but 192.168.2.50 is not.

The Algorithm

The check involves bitwise operations:

1. Convert IP to integer
2. Convert network address to integer
3. Create netmask from prefix length
4. Check: (IP & netmask) == (network & netmask)

Using the IP in Network API

TinyFn provides a simple endpoint for network membership checks:

POST https://api.tinyfn.io/v1/ip/in-network
Headers: X-API-Key: your-api-key
Content-Type: application/json

{
  "ip": "192.168.1.100",
  "network": "192.168.1.0/24"
}

{
  "ip": "192.168.1.100",
  "network": "192.168.1.0/24",
  "in_network": true,
  "network_address": "192.168.1.0",
  "broadcast_address": "192.168.1.255"
}

Check Multiple Networks

POST https://api.tinyfn.io/v1/ip/in-network
{
  "ip": "10.0.5.25",
  "networks": [
    "10.0.0.0/8",
    "192.168.0.0/16",
    "172.16.0.0/12"
  ]
}

Parameters

Code Examples

JavaScript / Node.js

const response = await fetch(
  'https://api.tinyfn.io/v1/ip/in-network',
  {
    method: 'POST',
    headers: {
      'X-API-Key': 'your-api-key',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      ip: '192.168.1.100',
      network: '192.168.1.0/24'
    })
  }
);
const { in_network } = await response.json();
console.log(in_network ? 'IP is in network' : 'IP is not in network');

Python

import requests

response = requests.post(
    'https://api.tinyfn.io/v1/ip/in-network',
    headers={'X-API-Key': 'your-api-key'},
    json={
        'ip': '192.168.1.100',
        'network': '192.168.1.0/24'
    }
)
result = response.json()
print('In network' if result['in_network'] else 'Not in network')

cURL

curl -X POST "https://api.tinyfn.io/v1/ip/in-network" \
  -H "X-API-Key: your-api-key" \
  -H "Content-Type: application/json" \
  -d '{"ip": "192.168.1.100", "network": "192.168.1.0/24"}'

Common Use Cases

• Access Control: Restrict access to specific IP ranges
• Rate Limiting: Apply different limits based on IP origin
• Geo-restrictions: Check if IPs are from certain regions
• Network Segmentation: Verify traffic is from expected networks
• Cloud Detection: Identify if requests come from cloud provider ranges

Best Practices

1. Batch checks: Use the multiple networks option for efficiency
2. Cache results: Cache network membership for frequently checked IPs
3. Order matters: Check most likely networks first for early exits
4. Handle edge cases: Consider broadcast and network addresses

Use via MCP

Your AI agent can call this tool directly via Model Context Protocol — no HTTP code needed. Add TinyFn to Claude Desktop, Cursor, or any MCP client:

{
  "mcpServers": {
    "tinyfn-ip": {
      "url": "https://api.tinyfn.io/mcp/ip/",
      "headers": {
        "X-API-Key": "your-api-key"
      }
    }
  }
}

See all ip address tools available via MCP in our IP Address MCP Tools for AI Agents guide.