I am studying for CCNA. In my book I read that wireless access points belong to OSI layer 2. I did some research and I found that is correct. This raised lots of questions in my head so I hope I don't get on your nerves 😛
I know that these devices are connected to switches or routers, I also know that AP's use CSMA-CA (at layer 2).
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Is this the only reason why they are Layer 2?
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Is there some kind of switching table inside the AP where it associates MAC's with output interfaces? What logical stuff does an AP have inside it? I ask this because if it has to forward packets it has to choose whether to send to the air or to the switch or router direclty connected to it.
Best Answer
Strictly speaking, access points are a L2 device. Their primary function is to bridge 802.11 WLAN traffic to 802.3 Ethernet traffic.
However, in the real world, enterprise wireless vendors often push more functionality to either the AP itself and/or tie them into a controller, with the end result that they often incorporate functionality from higher layers as well.
I don't entirely follow #1, but neither the connection to a switch or router nor the use of CSMA-CA has anything to do with their function as a L2 device. It is a L2 device because that is the layer of the network where it is designed to function. It doesn't care nor need L3 or above to operate and allow devices to communicate (again strictly speaking).
As for #2, yes, an AP (or any bridge) needs to keep track of which interface any individual device is connected. In general (and simply), they work on the principle of frames destined to an associated station gets forwarded out the wireless interface and any other frames get forwarded out the wired interface (or sent to the controller).