Generate a random IP address

Return a random IPv4 address from the ranges reserved for documentation.

JavaScriptNode.js & browsers Version 1.0.0 · MIT · .md

function randomDocumentationIp() {
  const networks = ['192.0.2', '198.51.100', '203.0.113'];
  return `${networks[Math.floor(Math.random() * networks.length)]}.${Math.floor(Math.random() * 254) + 1}`;
}

Usage

const ip = randomDocumentationIp();
['192.0.2', '198.51.100', '203.0.113'].includes(ip.split('.').slice(0, 3).join('.')); // → true
randomDocumentationIp(); // e.g. '203.0.113.42'

Lines marked → were executed in Node.js 22 and in headless Chromium, and each result was compared with the value shown. Lines marked e.g. are illustrative.

Know the limits

• RFC 5737 reserves 192.0.2.0/24, 198.51.100.0/24 and 203.0.113.0/24 for documentation. They never belong to a real host, so fixtures and logs in examples cannot point at one.
• The original drew any address: Math.floor(Math.random() * 255) never produced 255, and results included private, loopback and multicast ranges.
• For IPv6 examples, RFC 3849 reserves 2001:db8::/32.

The function above is the code the usage lines run. It does not validate its arguments; add checks where it receives untrusted input.

Keep exploring

• Generate a random boolean — Return true or false with equal probability.
• Generate a random floating point number in given range — Scale Math.random into [min, max).
• Generate a random hex color — Return a #rrggbb color from 24 random bits.