Re: [RFC] mac80211 rx filter in mesh mode, rt2x00 mesh point operation

[Ivo van Doorn <ivdoorn@gmail.com>]

On Friday 24 October 2008, Javier Cardona wrote:
> Andrey,
>=20
> On Thu, Oct 23, 2008 at 2:49 PM, Andrey Yurovsky <andrey@cozybit.com>=
 wrote:
> > I've come across a problem with the RX filter setting while testing=
 mesh point
> > operation in the rt2x00 driver (my hardware is rt73usb).  We transm=
it and
> > receive mesh beacons but mesh peer link action frames are dropped. =
 A patch
> > for enabling mesh point mode is included here, this works except th=
at:
> >
> > The RX filter, as set by mac80211 in mesh mode is 0x02, that is FIF=
_ALLMULTI is
> > set.  This is sufficient for other drivers but not for rt2x00.  I n=
oticed that
> > running tcpdump on the MP interface sets the filter to 0x43, this a=
dds
> > FIF_OTHER_BSS and FIF_PROMISC_IN_BSS, and rt2x00 is then able to ma=
ke peer
> > links and mesh point mode works correctly.
> >
> > Actually for rt2x00, setting either FIF_OTHER_BSS or FIF_PROMISC_IN=
_BSS is the
> > key here because they are both treated as FIF_PROMISC_IN_BSS, which=
 causes the
> > driver to enable TXRX_CSR0_DROP_TO_DS.
>=20
> Mesh frames have 4 addresses and no BSSID, so BSSID filtering should
> be disabled (i.e. FIF_OTHER_BSS should be set).
> The ALL_MULTI flag is also needed for mesh mode because an
> intermediate node has to forward multicast traffic for addresses that
> it may not be listening to.
>=20
> But promiscuous mode is not necessary:  mesh points don't need to
> receive unicast frames not addressed=B9 to them.  Furthermore, enabli=
ng
> promiscuous mode normally disables acknowledgments, which are needed
> for proper mesh operation.
>=20
> So my recommendation would be to configure the RX filter in mesh mode
> to be ( FIF_ALLMULTI | FIF_OTHER_BSS )

=46or rt2x00 this would turn into:
	FIF_ALLMULTI | FIF_OTHER_BSS | FIF_PROMISC_IN_BSS

because it cannot filter on other BSS, but this conversion is within rt=
2x00
based on capabilities by the driver. So as long as mac80211 provides th=
e flags
it wants (FIF_ALLMULTI | FIF_OTHER_BSS), rt2x00 will convert it to the =
flags that
make sure those frames will at least get through (FIF_ALLMULTI | FIF_OT=
HER_BSS | FIF_PROMISC_IN_BSS),
including some additional noise from frames mac80211 didn't request spe=
cifically,
but those can be filtered out in mac80211.

Ivo
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