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diff --git a/cluster-geo/README.md b/cluster-geo/README.md
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+Cluster GeoIP Service
+======
+
+In cluster mode (build with ZT\_ENABLE\_CLUSTER and install a cluster definition file), ZeroTier One can use geographic IP lookup to steer clients toward members of a cluster that are physically closer and are therefore very likely to offer lower latency and better performance. Ordinary non-clustered ZeroTier endpoints will have no use for this code.
+
+If a cluster-mode instance detects a file in the ZeroTier home folder called *cluster-geo.exe*, it attempts to execute it. If this program runs, it receives IP addresses on STDIN and produces lines of CSV on STDOUT with the following format:
+
+    IP,result code,latitude,longitude,x,y,z
+
+The first field is the IP echoed back. The second field is 0 if the result is pending and may be ready in the future or 1 if the result is ready now. If the second field is 0 the remaining fields should be 0. Otherwise the remaining fields contain the IP's latitude, longitude, and X/Y/Z coordinates.
+
+ZeroTier's cluster route optimization code only uses the X/Y/Z values. These are computed by this cluster-geo code as the spherical coordinates of the IP address using the Earth's center as the point of origin and using an approximation of the Earth as a sphere. This doesn't yield *exact* coordinates, but it's good enough for our purposes since the goal is to route clients to the geographically closest endpoint.
+
+To install, copy *cluster-geo.exe* and the *cluster-geo/* subfolder into the ZeroTier home. Then go into *cluster-geo/* and run *npm install* to install the project's dependencies. A recent (4.x or newer) version of NodeJS is recommended. You will also need a [MaxMind GeoIP2 Precision Services](https://www.maxmind.com/) license key. The *MaxMind GeoIP2 City* tier is required since this supplies actual coordinates. It's a commercial service but is very inexpensive and offers very good accuracy for both IPv4 and IPv6 addresses. The *cluster-geo.js* program caches results in a LevelDB database for up to 120 days to reduce GeoIP API queries.
diff --git a/cluster-geo/cluster-geo.exe b/cluster-geo/cluster-geo.exe
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+++ b/cluster-geo/cluster-geo.exe
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+#!/bin/bash
+
+export PATH=/bin:/usr/bin:/usr/local/bin:/sbin:/usr/sbin
+
+cd `dirname $0`
+if [ ! -d cluster-geo -o ! -f cluster-geo/cluster-geo.js ]; then
+	echo 'Cannot find ./cluster-geo containing NodeJS script files.'
+	exit 1
+fi
+
+cd cluster-geo
+
+exec node --harmony cluster-geo.js
diff --git a/cluster-geo/cluster-geo/cluster-geo.js b/cluster-geo/cluster-geo/cluster-geo.js
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+++ b/cluster-geo/cluster-geo/cluster-geo.js
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+"use strict";
+
+//
+// GeoIP lookup service
+//
+
+// GeoIP cache TTL in ms
+var CACHE_TTL = (60 * 60 * 24 * 120 * 1000); // 120 days
+
+// Globally increase event emitter maximum listeners
+//var EventEmitter = require('events');
+//EventEmitter.prototype._maxListeners = 1000;
+//process.setMaxListeners(1000);
+
+// Load config
+var config = require(__dirname + '/config.js');
+
+if (!config.maxmind) {
+	console.error('FATAL: only MaxMind GeoIP2 is currently supported and is not configured in config.js');
+	process.exit(1);
+}
+var geo = require('geoip2ws')(config.maxmind);
+
+var cache = require('levelup')(__dirname + '/cache.leveldb');
+
+function lookup(ip,callback)
+{
+	cache.get(ip,function(err,cachedEntryJson) {
+		if ((!err)&&(cachedEntryJson)) {
+			try {
+				let cachedEntry = JSON.parse(cachedEntryJson.toString());
+				if (cachedEntry) {
+					let ts = cachedEntry.ts;
+					let r = cachedEntry.r;
+					if ((ts)&&(r)) {
+						if ((Date.now() - ts) < CACHE_TTL) {
+							r._cached = true;
+							return callback(null,r);
+						}
+					}
+				}
+			} catch (e) {}
+		}
+
+		geo(ip,function(err,result) {
+			if (err)
+				return callback(err,null);
+			if ((!result)||(!result.location))
+				return callback(new Error('null result'),null);
+
+			cache.put(ip,JSON.stringify({
+				ts: Date.now(),
+				r: result
+			}),function(err) {
+				if (err)
+					console.error('Error saving to cache: '+err);
+				return callback(null,result);
+			});
+		});
+	});
+};
+
+var linebuf = '';
+process.stdin.on('readable',function() {
+	var chunk;
+	while (null !== (chunk = process.stdin.read())) {
+		for(var i=0;i<chunk.length;++i) {
+			let c = chunk[i];
+			if ((c == 0x0d)||(c == 0x0a)) {
+				if (linebuf.length > 0) {
+					let ip = linebuf;
+					lookup(ip,function(err,result) {
+						if ((err)||(!result)||(!result.location)) {
+							return process.stdout.write(ip+',0,0,0,0,0,0\n');
+						} else {
+							let lat = parseFloat(result.location.latitude);
+							let lon = parseFloat(result.location.longitude);
+
+							// Convert to X,Y,Z coordinates from Earth's origin, Earth-as-sphere approximation.
+							let latRadians = lat * 0.01745329251994; // PI / 180
+							let lonRadians = lon * 0.01745329251994; // PI / 180
+							let cosLat = Math.cos(latRadians);
+							let x = Math.round((-6371.0) * cosLat * Math.cos(lonRadians)); // 6371 == Earth's approximate radius in kilometers
+							let y = Math.round(6371.0 * Math.sin(latRadians));
+							let z = Math.round(6371.0 * cosLat * Math.sin(lonRadians));
+
+							return process.stdout.write(ip+',1,'+lat+','+lon+','+x+','+y+','+z+'\n');
+						}
+					});
+				}
+				linebuf = '';
+			} else {
+				linebuf += String.fromCharCode(c);
+			}
+		}
+	}
+});
+
+process.stdin.on('end',function() {
+	cache.close();
+	process.exit(0);
+});
diff --git a/cluster-geo/cluster-geo/config.js.sample b/cluster-geo/cluster-geo/config.js.sample
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+++ b/cluster-geo/cluster-geo/config.js.sample
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+// MaxMind GeoIP2 config
+module.exports.maxmind = {
+	userId: 1234,
+	licenseKey: 'asdf',
+	service: 'city',
+	requestTimeout: 1000
+};
diff --git a/cluster-geo/cluster-geo/package.json b/cluster-geo/cluster-geo/package.json
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+++ b/cluster-geo/cluster-geo/package.json
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+{
+  "name": "cluster-geo",
+  "version": "1.0.0",
+  "description": "Cluster GEO-IP Query Service",
+  "main": "cluster-geo.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "ZeroTier, Inc.",
+  "license": "GPL-3.0",
+  "dependencies": {
+    "geoip2ws": "^1.7.1",
+    "leveldown": "^1.4.2",
+    "levelup": "^1.3.0"
+  }
+}