Hi,I'm just wondering how a pc with a 802.11 interface send and receive traffice from the net. Documents say that it uses its 802.11 interface mac as its source and the ap's mac as its destination. This is what puzzles me. If I type arp -a from the client PC, I can only see the gateway's mac (that's what I think is right), no ap's mac. So why and how does the client PC send traffic to ap's mac?
That's a pretty broad question - I would recommend reading Matthew Gast's "802.11 Wireless Networks - The Definitive Guide". The short answer is that there are 4 address fields usable in an 802.11 data packet.
From the book:
Frames destined for an access point take their source/transmitter address from the network interface in the wireless station. Access points do not perform filtering, but instead use the third address to forward data to the appropriate location in the distribution system.
Think of an AP like a switch. If you have a client connected to a switch, it uses its own MAC as the source, but it doesn't use the switch as the destination. The destination is the target client's MAC is it's a local transmission, or the default gateway if it's sending traffic to a different subnet.
Wireless works the same way. The destination MAC address is either the receiving client or default gateway. It does not use the AP MAC as the destination.
I hope that helps, and please let me know if you have more questions.
EDIT: Haha, overlapped with Rob again. We seem to do that a lot in these forums, Rob! +5 for the additional info.
Thank you guys.I have read the book refered by you guys. This is what I concluded: Right the pc use its mac as source and the client's or the default gate's mac as its destination. However before frames reach ethernet, they are 802.11 frames so their frame formats are different from that of wired ethernet. There are commonly used three types of mac addresses. The client uses the address 1, which is the mac address (or BSSID) of the AP, as its receiver address; address 2, as its source address;address 3, which is the mac address of the gateway, as destination address. And , after the AP reveives the frame, it use the address 2 as source, address 3 as destination, transforms 802.11 frame into ethernet frame. And then the frame goes into wired net.