[removed] Is IP In One Of These Subnets?

Question

So I have ~12600 subnets:

eg. 123.123.208.0/20

and an IP.

I can use a SQLite Database or an array or whatever

There was a similar question asked

Answer 1

Keywords: Binary searching, preprocessing, sorting

I had a similar problem and binary search appears to be very efficient if you can pre-process your subnet list and sort it. Then you can achieve an asymptotic time complexity of O(log n).

Here's my code (MIT License, original location: https://github.com/iBug/pac/blob/854289a674578d096f60241804f5893a3fa17523/code.js):

function belongsToSubnet(host, list) {
  var ip = host.split(".").map(Number);
  ip = 0x1000000 * ip[0] + 0x10000 * ip[1] + 0x100 * ip[2] + ip[3];

  if (ip < list[0][0])
    return false;

  // Binary search
  var x = 0, y = list.length, middle;
  while (y - x > 1) {
    middle = Math.floor((x + y) / 2);
    if (list[middle][0] < ip)
      x = middle;
    else
      y = middle;
  }

  // Match
  var masked = ip & list[x][1];
  return (masked ^ list[x][0]) == 0;
}

And an example usage:

function isLan(host) {
  return belongsToSubnet(host, LAN);
}

var LAN = [
  [0x0A000000, 0xFF000000], // 10.0.0.0/8
  [0x64400000, 0xFFC00000], // 100.64.0.0/10
  [0x7F000000, 0xFF000000], // 127.0.0.0/8
  [0xA9FE0000, 0xFFFF0000], // 169.254.0.0/16
  [0xAC100000, 0xFFF00000], // 172.16.0.0/12
  [0xC0A80000, 0xFFFF0000]  // 192.168.0.0/16
];

isLan("127.12.34.56"); // => true
isLan("8.8.8.8"); // => false (Google's Public DNS)

You can get a PAC script* and see how it performs (it loads a China IP list from somewhere else, sorts them and formats them appropriately) against 5000s of subnets. In practice its speed is surprisingly satisfactory.

The preprocessing code can be inspected using F12 Dev Tools on the above page. In short, you need to convert 1.2.3.4/16 to [0x01020304, 0xFFFF0000], i.e. 32-bit unsigned integer for the IP address and network mask.

^{* Link goes to my personal website.}