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I have a LAN network with three computers connecting to the Internet both through wired and encrypted wifi connections. Is there a way I can check who is connecting to the Internet via the wifi connection?

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3  
What wireless router/access point do you have? I know my dlink will let me look at that through it's web interface. –  mikeazo Dec 20 '11 at 12:15
    
It's the router my isp provides, not sure who the manufacturer is... –  Jane Dec 28 '11 at 16:27
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3 Answers

up vote 4 down vote accepted

On the wireless routers I'm familiar with, there is an admin page that lists the MAC addresses of devices that are connected. Take this with a grain of salt: a malicious user could easily change the MAC address (to either look like one of your devices, or so that it appears to be a completely different device each time he connects).

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Great - thanks for the tip! –  Jane Dec 28 '11 at 16:21
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In general, most wireless routers will offer an admin page as per @bstpierre's answer. An alternative on higher end routers is to use SNMP (have a look at this blog post for some information) - which can make it easier to script for automated stats/alerting.

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Of course, this requires that all of the computers on your network are under your administrative control. –  Iszi Dec 20 '11 at 13:42
    
It would help, although even just pulling off the router info through SNMP could be informative. –  Rory Alsop Dec 20 '11 at 13:44
    
Thank you for your help, Rory. –  Jane Dec 28 '11 at 16:24
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It might be helpful to know the purpose of the connection data. The AP will have logs, you could poll the computer's interfaces for activity, or you could set up a monitor on the wifi.

Cace Technology (now Riverbed) has Cascade Pilot that can be used (with a wireless packet capture nic) to monitor wifi activity. That way you can know who is connecting, even if it is not those 3 expected hosts. There are also built-in reporting and monitoring features.

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Thank you, Schroeder. –  Jane Dec 28 '11 at 16:25
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