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I am very paranoid about wireless connections and someone stealing my broadband bandwidth, which could lead to worse things.

My question is, how can I detect if my broadband bandwidth is being stolen?

I have a Belkin SURF+ N300 wireless router.

Ideally, it would be cool if I would get alerted automatically, but if that is not possible, then a manual process would be fine.

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Why don't you just enable WPA2 security with a strong password? – Spiff Jul 22 '11 at 18:42
@Spiff ... because that isn't flawless or foolproof. I wholeheartedly endorse the idea of using WPA2, mind you. – CarlF Jul 22 '11 at 19:22
This was posted to Ask Ubuntu first and was erroneously migrated (as off-topic). I say erroneously because it's possible to answer this solely from Ubuntu's perspective (which I since have). Not sure what you want to do with this thread but perhaps it could be opened up to cater for other operating systems. – Oli Jul 22 '11 at 20:10
As my brother using Windows, it would be good if he can have a solution to help track such events. – oshirowanen Jul 22 '11 at 20:13
@CarlF: Of course it isn't flawless. Nor is any other plan or solution that exists. Giving another solution that has flaws doesn't solve the problem. Solving the problem is changing the perspective of the user. – surfasb Jul 22 '11 at 23:19
up vote 4 down vote accepted

You should mention what OS you're using. Anyway, assuming you're referring to someone using your bandwith via your wireless router, the simplest way to monitor that is to keep a record of all devices that have connected to your N300 router.

I had a quick look at the N300 user manual and found no mention of SNMP support, so you would have to log on to the web interface and check what devices are currently connected, or possibly have the router email you logs on daily basis. You could then easily parse the logs and have a simple list of connected DHCP clients for any given day from which it'd be easy to spot any devices that didn't belong there. Little bit of shell scripting and you could automate it, or you could just collect the logs for a few days and see if there's been any unwanted visitors.

Provided that you've changed the default admin password, any prospective bandwith stealer would probably have hard time avoiding being logged.

Or, in case you don't trust the logs and wanted to take extreme measures, set up a box between the N300 and whatever it is connected to, and set it to monitor all traffic passing through it.

This has nothing to do with the question itself, but just as a sidenote, if you're using a WPA2 key over 10 characters long then no one is going to crack it. They could set up an AP to act as an evil-twin, and you might accidentally connect to that, but then they'd be stealing something other than bandwith. Even if they capture the handsake, the key itself, when strong and varied, would take many years to crack.

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"Many years" is a light way of putting it. Basically, the Sun would have turned into a Red giant, swallowing the earth by the time they crack the password. . . – surfasb Jul 22 '11 at 23:22
+1 For just looking at the screen that shows connected devices. – KCotreau Jul 23 '11 at 1:00
@surfasb, even with the power of GPUs? i.e. 4x GTX680 cards? – oshirowanen Jul 25 '11 at 11:51
Without a dictionary attack, there are exactly 63 valid ASCII characters to choose from for a WPA password. Thus, the number of possibilities is (63!)^10. Lets say you can test 1 million combinations a second (unlikely, LOL). It will still take you about 1 x 10^800 years. – surfasb Jul 25 '11 at 16:00

Check these two out: IP Scanner and Network Monitor

They have some neat features like tracking the computers on your network etc.

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