2.js

var fs = require('fs');

var c = {};

fs.readFile('ips', function(err, data) {
	var ips = data.toString().split('\n');

	for (var i in ips) {
		if (!c[ips[i]]) {
			c[ips[i]] = 1
		} else {
			c[ips[i]]++;
		}
	}

	var u = {};

	for (var i in c) {
		if (c[i] > 500) {
			u[i] = c[i];
			console.log(i);
		}
	}
});