Ethernet over Wi-Fi

[hostettle]

Hi,

Pleased, could anyone confirm this ?

When we have a MAC 802.3 frame over a MAC 802.11 frame, we can suppose that the MAC 802.3 frame is totally put inside the "Frame Body" of the MAC 802.11 (the payload).

So, it would seem that the DA / SA addresses of the MAC 802.3 frame are fully independant from the DA / SA addresses of the MAC 802.11 frame. We know that the 802.11 frame has 3 or 4 addresses, the question is just for the DA and SA addresses (e.g. table 8-19 of IEEE 802.11-2012).

Perhaps, if you have a capture, it would be interesting.

Thanks,

best regards,

Michel

[Amjad Abdullah · Accepted solution]

Hi Mike,

No of course the full 802.3 is not being put inside 802.11 fram. this will be a kind of tunneling which is not used.

What is being used is only the frame payload. the header is removed and another header is being put.

The 4 addresses that are being used in 802.11 frame (in most situations 3 of them are only being used) are being put for specific purpose due to 802.11 media specificity. Becaue there will be usually an AP for clients to communicate, the AP address (BSSID) is usually used beside sender and receiver addresses to decide what AP is actually should handle this frame. Imagine more than one AP is being used with same SSID, how will we know which AP will handle the frame from the sender and forward it to the receiver? we have no way to know if we do not have some kind of ID to distinguish which AP should handle the frame.

If a wireless client wants to communicate with a wired client on same VLAN/Subnet, then the mapping of mac addresses will include only the sender/receiver addresses in the 802.3 frame. It will not contain the BSSID. The AP -if autonomous network- or wireless controller -if unified network- will do the mapping. In case of a wired client is sending to the wireless client (on same VLAN), The MAC address of the destaned client will be used as destination and the AP (or wireless controller) will do the mapping and add hte BSSID (third mac address) to the 802.11 frame where it is needed.

Allow me to thank you for your good question.

Amjad

[hostettle]

Hi Amjad,

Thanks for your time, your very good synthesis.

> No of course the full 802.3 is not being put inside 802.11 fram.

> this will be a kind of tunneling which is not used.

In wired LAN, this kind of tunneling is used in the PLC technology (Powerline communication) specified in IEEE 1901-2010. It is also used in Bluetooth in IEEE 802.15.1: as far as I know, we have MAC 802.3 over BNEP.

But you're right, to transmit a MAC 802.3 frame over Wi-Fi, the header is removed and replaced by (1) a MAC 802.11 header with DA and SA addresses, (2) a specific LLC header that takes the L/T and TAG information.

It is also a similar mechanism in the A-MSDU structure (Aggregated MAC SDU) where several MAC 802.3 frames can be inserted in a single MAC 802.11.

> Allow me to thank you for your good question.

And thank for your previous reply. You can add comments if you want.

Best regards,

Michel

[Amjad Abdullah]

Hi Mike,

I was only talking about 802.11-802.3 tunneling which is not being used. I am not actually aware about other technologies that might use tunneling.

It seems you know about the situation better than me.

Thank you.

Amjad

[hostettle]

Hi Amjad,

Thanks for the comments.

> It seems you know about the situation better than me.

It's just an impression. This talking gave me the opportunity to clarify, to clean ideas.

You made me progress in my understanding!

Best regards,

Michel