How would you compare IP address?

Question

For my server app, I need to check if an ip address is in our blacklist.

What is the most efficient way of comparing ip addresses? Would converting the IP address to integer and comparing them efficient?

Answer 1

The following one is I've used in JavaScript

function isValidIPv4Range(iPv4Range = '') {
  if (IP_V4_RANGE_REGEX.test(iPv4Range)) {
    const [fromIp, toIp] = iPv4Range.split('-');

    if (!isValidOctets(fromIp) || !isValidOctets(toIp)) {
      return false;
    }

    const convertToNumericWeight = ip => {
      const [octet1, octet2, octet3, octet4] = ip.split('.').map(parseInt);

      return octet4 + (octet3 * 256) + (octet2 * 256 * 256) + (octet1 * 256 * 256 * 256);
    };

    return convertToNumericWeight(fromIp) < convertToNumericWeight(toIp);
  }
  return false;
}

Answer 2

Depends what language you're using, but an IP address is usually stored as a 32-bit unsigned integer, at least at the network layer, making comparisons quite fast. Even if it's not, unless you're designing a high performance packet switching application it's not likely to be a performance bottleneck. Avoid premature optimization - design your program for testability and scalability and if you have performance problems then you can use a profiler to see where the bottlenecks are.

Edit: to clarify, IPv4 addresses are stored as 32-bit integers, plus a netmask (which is not necessary for IP address comparisons). If you're using the newer and currently more rare IPv6, then the addresses will be 128 bits long.