[Battlemesh] the relationship of BSSID to anything...

[Gui Iribarren]

On 06/09/2013 08:52 PM, Dave Taht wrote:
> while at battlemesh, someone in the batman part mumbled at me that I
> should set the BSSID to the same (but different from the other networks
> in play that week) across
> my entire babel mesh network because [mumble, mumble] and that on larger
> meshes you can
> end up with parts not communicating with each due to [mumble, mumble]
> unless you did that.

The essid you set ("babel") is only sent in adhoc beacons, which are 
basically informative.
the header that is used to address/identify data packets (i.e. what 
matters) only includes the *BSSID* ("cell id").

what's the essid for, then?
Well, if you don't set a specific Bssid, when the router boots up it 
will scan the air and try to spot an adhoc beacon from a neighbour, 
containing both the Essid you told it ("babel") and a Bssid, so it will 
"join" that cell.
If it gets no beacon, (...an avian carrier collided with the signal?) it 
will just invent a random Bssid, creating a new cell.
Avian carrier gone, nodes could communicate again physically, but as 
they don't agree on the Bssid, packets get dropped by the card, and you 
just got your network "bifurcated"

Morale: for adhoc, force a Bssid, and the Essid then becomes irrelevant

(i.e. you can even have each node broadcasting its beacons with 
*different ESSIDs*, as we did at the battlemesh, since no-one will pay 
attention to them, as every node already knows the BSSID it should use)

real-world working example with two nodes:

NODE1

wireless. at wifi-iface[2]=wifi-iface
wireless. at wifi-iface[2].device=radio1
wireless. at wifi-iface[2].encryption=none
wireless. at wifi-iface[2].network=mesh1
wireless. at wifi-iface[2].mode=adhoc
wireless. at wifi-iface[2].bssid=02:15:7a:d6:d5:b6
wireless. at wifi-iface[2].ssid=whatever-foo

NODE2

wireless. at wifi-iface[2]=wifi-iface
wireless. at wifi-iface[2].device=radio1
wireless. at wifi-iface[2].encryption=none
wireless. at wifi-iface[2].network=mesh1
wireless. at wifi-iface[2].mode=adhoc
wireless. at wifi-iface[2].bssid=02:15:7a:d6:d5:b6
wireless. at wifi-iface[2].ssid=whatever-bar

> I happen to have an ever larger babel mesh which periodically
> bifurbicates. A core radio stops
> communicating with half the network, for some reason. I'd long thought
> it was a layer 3 problem of some sort,
> but perhaps it's related to this BSSID issue? Which I don't understand?
> (help?)

I only hope I haven't obscured it even further :)

Cheers!!

Gui