Monitor router aggregate bandwith usage via SNMP

/*	Monitors aggregate bandwith directly from your router via SNMP

	Public Domain.

	Author: http://joonas.fi/

	2014-03-09

	Output:

		15 kB/s
		28 kB/s
		8 kB/s
		6 kB/s
		...

	Requires node.js. This script is cross platform.

	The only dependency is snmp-native NPM module. To install:

	$ npm install snmp-native

	You may have to specifically enable SNMP from your router: http://imgur.com/hAzn2hZ

	This simply dumps kB/s values, but you can use this to build something fancier.
*/
var snmp = require('snmp-native');

var config = {
	routerAddr: '10.10.100.100',
	routerSnmpPort: 161, // most likely the right one
	readCommunity: 'public', // usually "public". a.k.a. password - rather stupid terminology
	pollingIntervalMs: 2500, // interval for measurements [milliseconds]

	// there may be multiple entries in the snmp interface table
	// if 0 does not work for you, try 1, 2 and so on..
	snmpInterfaceIndex: 0
};

// Create a Session with explicit default host, port, and community.
var snmpSession = new snmp.Session({
	host: config.routerAddr,
	port: config.routerSnmpPort,
	community: config.readCommunity
});

// this variable holds previous measurement from SNMP so we can calculate delta for it
var previousMeasurement = null;

var snmpQueryResult = function (err, result){
	if (err) {
		console.log('error: ' + err);
		return;
	}

	var ifOutOctets = result[config.snmpInterfaceIndex];

	// first iteration => store measurement right away as previous
	if (previousMeasurement === null) {
		previousMeasurement = ifOutOctets;
	}

	// calculate delta
	var delta = {
		value: ifOutOctets.value - previousMeasurement.value,
		receiveStamp: ifOutOctets.receiveStamp - previousMeasurement.receiveStamp
	};

	// store current measurement as previous, so next iteration gets delta
	previousMeasurement = ifOutOctets;

	// cannot compute kbs/sec since receive delta time is zero
	if (delta.receiveStamp == 0) {
		return;
	}

	var octetsPerSec = delta.value / delta.receiveStamp * 1000;

	var kilobytesPerSec = octetsPerSec / 1024;

	console.log(Math.round(kilobytesPerSec) + ' kB/s');
};

// here is the actual business:
// - this function is called every pollingIntervalMs milliseconds
// - it polls the router via SNMP protocol for the variable that holds total inbound octets
// - by calculating deltas for the total and timestamps we can calculate kilobytes/sec
var pollResult = function () {
	/* inbound traffic:

			.1.3.6.1.2.1.2.2.1.10
			.iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifInOctets

		outbound traffic:

			.1.3.6.1.2.1.2.2.1.16
			.iso.org.dod.internet.mgmt.mib-2.interfaces.ifTable.ifEntry.ifOutOctets
	*/
	snmpSession.getSubtree({
		oid: [1, 3, 6, 1, 2, 1, 2, 2, 1, 10]
	}, snmpQueryResult);

	// schedule us to be executed again
	setTimeout(pollResult, config.pollingIntervalMs);
};

// get this shit started
pollResult();