how does AP see WLAN clients

April 6, 2009 at 00:43:31
Specs: Linux
Hi all,

Could any tell me how does an access point(without NAT tables) know the clients in vicinity? I am not asking in terms of radio signal reception but what I want to know is, does the AP maintain a table/list structure with the SSID of clients or its MAC address or its IP address? If yes where does it keep it?(in the sense, in which file system of its OS?)

Also, a wireless router operates at netwok layer level maintaing NAT tables and inspecting packets at that level and routing IP packets. I assume in both wireless router case and AP#s case they must do the client detection at the physical layer level.

How does this detection recored before sending the packets higher up the stack in case of wireless router?

I assume in case of AP, it just detects clients and routes the WLAN packet directly to client. Is this true?

It is important for me to know this as we want to tweak the AP/wireless router for some security needs.

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April 6, 2009 at 07:13:02
A wireless router or AP doesn't look for the clients, the clients look for the them. The client requests an IP address. It's only after the request is answered, that the router adds the IP & MAC addresses to it's list.

To secure a wireless router, first change the default password & enable encryption. WPA is much harder to crack than WEP because handshakes must be captured instead of IVs (initialization vectors). Either way, MAC filtering should be enabled. That way the router will discard packets from MAC addresses not in it's table. Also, I prefer static IP addresses for the simple reason that if the encryption is cracked, the router can't give an IP address to the cracker because DHCP isn't running. The MAC filtering helps with that too.

As a side note, I've found that Actiontec routers, used by Verizon are the easiest to crack. All of the above precautions should be used, especially with them.

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