Traffic accounting with SNMP and Python on Windows

If you're not on a flat-rate ISP data-plan, and your ISP made you pay extra last month such as myself :) You might be interested in monitoring your home bandwidth. A nifty little features of most routers or ADSL modems, is support for SNMP. Since both me and my old folks use the same ADSL line, any host based monitoring solution wouldn't really work. I had to monitor the usage using SNMP. Since my folks are using Windows, the solution had to work on that. The solution overview is:

1- Enable SNMP on ADSL modem
2- Use a windows scheduled task to run a windows Batch file, that uses SNMP-tools for windows to pull data from the router
3- Use a windows scheduled task to run a python script that processes the batch file output and computes the total traffic

Data from the batch files are written in a file signifying the current month (example 05.txt for May). Here is the code for the batch file

cd e:\traffic

e:\

FOR /F "TOKENS=1* DELIMS= " %%A IN ('DATE/T') DO SET CDATE=%%B

FOR /F "TOKENS=1,2 eol=/ DELIMS=/ " %%A IN ('DATE/T') DO SET mm=%%B



echo %mm%

snmpget.exe -c public -O v -v 1 192.168.11.1 .1.3.6.1.2.1.2.2.1.10.12 >> %mm%.txt

 

Note that the IP 192.168.11.1 should be replaced with the internal IP of your ADSL router. Also, the SNMP OID .1.3.6.1.2.1.2.2.1.10.12 (symbolically: IF-MIB::ifInOctets.12) is the incoming octets on network interface "12". You might need to change that last "12" to represent your network topology. You can use the "snmpwalk" command to list your interface names like:

snmpwalk -c public -v1 192.168.11.1
this yields
...
IF-MIB::ifDescr.12 = STRING: ppp0
...

I know that my ppp0 is the link to my ISP, so that's the interface I used

And here is the code for the python script

# -*- coding: utf-8 -*-

import glob

import locale

import os

locale.setlocale(locale.LC_ALL, '')

reports = sorted(glob.glob('??.txt'))

totalsReport = open('totals.txt','w')

totalsReport.write(' Month      Traffic \n')

totalsReport.write('====================\n')

for report in reports:

        datastring = open(report,'r').readlines()

        data = [ int(datastring[i].strip().split()[1]) for i in range(len(datastring)) ]

        diff = [ data[i+1] - data[i] for i in range(len(data) - 1) ]

        trafficDeltas = [ (data[i+1],diff[i])[diff[i] > 0] for i in range(len(diff)) ]

        totalTraffic = sum(trafficDeltas)

        totalsReport.write(' %s => %s \n'% (report.replace('.txt','') , locale.format('%d', totalTraffic, True)) )



totalsReport.close()

Glancing over the Python code, you can already see I'm a list comprehension addict :) The code reads the snmp bytes values from ??.txt (example: 05.txt), computes bandwidth deltas, handles counter resets (32bit overflow, or router loosing power) and computes totals. Then writes the total to a file named "totals.txt"

This solution is resistant to the router loosing power and resetting its internal traffic counter back to zero. This is because the data is continuously being saved to non-volatile medium (PC's hard-disk). Also, the Windows PC running those two scripts, does NOT need to be running 24x7 .. Just most of the time. If however the PC is powered off, AND the modem power cycles or hangs, you might loose some accuracy, the results will still be fairly valid though. Hope that's helpful to anyone out there