APs and multiple BSSID support (OT?)

Bob Carlson rjc at sigpro.com
Tue Feb 6 12:06:41 EST 2007


Perhaps this is a little OT, but this seems like a good community to which
to address this question. I'm using wpa_s in a Wifi client device that acts
like multiple virtual clients. One key problem is APs that support multiple
SSIDs. Atheros calls these virtual APs. Cisco doesn't call them anything,
they just refer to "multiple SSIDs". Unlike the Atheros code that I am
familiar with, Cisco allows multiple SSIDs on a single BSSID, but you can
enable multiple BSSIDs.

In the Atheros case, when more than one BSSID is needed, they generate it
using the private mac address space. They set the 0x02 bit in byte 0 of the
address to make it private and then add 1, 2 or 3 to the 0x0c bits in byte
0 to make up to 3 additional addresses. So you would have
06:06:C7:1F:0C:EC, and 00:06:C7:1F:0C:EC for example.

Cisco uses a more straightforward approach, just adding 1 to byte 5.
Presumably this means that they allocate many mac addresses to each device.
The device I am familiar with supports 8 BSSIDs and so would use the 0x07
bits in byte 5 for it's BSSIDs. For example, 2 BSSIDs would be
00:16:46:B8:97:60 and 00:16:46:B8:97:61.

Does anyone know of any other different methods of generating multiple
BSSID?

Thanks, Bob




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