VLAN/bridge "compression" in wifi (was: Re: [PATCH 3/8] qtnfmac: implement AP_VLAN iftype support)

+netdev

On Tue, 2017-09-05 at 15:45 +0200, Johannes Berg wrote:

In a way this feature seems mis-designed - you never have 802.1Q tags
over the air, but you're inserting them on RX and stripping them on
TX, probably in order to make bridging to ethernet easier and not
have to have 802.1Q acceleration on the ethernet port, or - well - in
order to have an ability to do this with an ethernet card that only
has a single CPU port.

Ok this isn't really right either - it's only for saving the 802.1Q
acceleration on the Ethernet port, really - and saving the extra
bridges.

To clarify, I think what you - conceptually - want is the following
topology:

        +--- eth0.1  ---  br.1  ---  wlan0.1
        |
eth0 ---+--- eth0.2  ---  br.2  ---  wlan0.2
        | 
        +--- eth0.3  ---  br.3  ---  wlan0.3

where eth0.N is just "ip link add link eth0 name eth0.N type vlan id N"
and br.N is obviously a bridge for each, and the wlan0.N are AP_VLAN
type interfaces that isolate the clients against each other as far as
wifi is concerned.

Is this correct? As far as I understand, that's the baseline topology
that you're trying to achieve, expressed in terms of Linux networking.

Now, you seem to want to compress this to

                  +---  wlan0.1
                  |
eth0  ---  br  ---+---  wlan0.2
                  |
                  +---  wlan0.3

and have the 802.1Q tag insertion/removal that's normally configured to
happen in eth0.N already be handled in wlan0.N.

Also correct?


We clearly don't have APIs for this, and I don't think it makes sense
in the Linux space - the bridge and wlan0.N suddenly have tagged
traffic rather than untagged, and the VLAN tagging is completely hidden
from the management view.

johannes