[Simh] Klh10 vs Simh

[Peter Svensson]

On Sun, 28 Feb 2016, Johnny Billquist wrote:

> On 2016-02-28 20:47, Peter Svensson wrote:
>>  Hi all,
>>
>>  There is a lot of incorrect information about the 802.11 capabilities
>>  going around on this list lately.
>>
>>  Normally 802.11 (all versions) uses 3 mac addresses instead of 4 to
>>  conserve capacity. This is purely a legacy issue from way back when.
>>  These addresses are used as follows.
>>
>>  - Station to AP:
>>     - AP MAC address (BSSID)
>>     - Station MAC address
>>     - 802.1 destination MAC address
>>     - (802.1 source address is copied from Station MAC field by the AP)
>>
>>  - AP to Station
>>     - Station MAC address
>>     - AP MAC address (BSSID)
>>     - 802.1 source MAC address (SA)
>>     - (802.1 dest address is copied from the Station MAC filed by the STA)
>
> Do I understand you right in that when you write 802.1 destination address, 
> you are in fact talking about the 802.2 frame destination MAC address?
>
> If so, this makes sense, it would match what I seem to have observed.

First of all, I am sorry for writing "802.1" when I meant "802.3". I was 
at least consistenly mistyping/misthinking throughout the whole email. 
Please substitute "802.3" whenever I wrote "802.1".

I am not sure what you mean by the 802.2 frame MAC address. The 802.2 
specification specifies the LLC which AFAIK does not include any 
addresses. It does include protocol type information. 802.2 LLC headers 
can sometimes be seen on on eathernet when using LLC+SNAP headers, but 
that is rare these days. Most Ethernet networks use the EtherType 
mechanism. 802.2 is still in use on some non-Ethernet networks, and 802.2 
LLC+SNAP in some more. I think (but I am not sure) that 802.11 uses 
802.2 LLC+SNAP instead of raw EtherType.

Anyway, the destination address is the 802.3 link layer destination 
address. I.e. the one we all think of as the "ethernet destination mac", 
the one used to filter out packets for "us" and by bridges for forwarding.

The Station MAC address is used by the 802.11 layer to handle filtering on 
RX, but also to properly indicate the endpoint of the wireless link to the 
other side. This is used by access control, authentication, RSSI and other 
cases where the AP needs to know whih STA (as opposed to final recipient 
MAC at the ethernet level) it is talking to.

Peter