[Bridge] Multicast packets are not bridged from ethernet to wireless interface

Stephen Hemminger stephen at networkplumber.org
Fri Jul 31 16:30:07 UTC 2015

On Fri, 31 Jul 2015 19:56:12 +0530
saurav barik <saurav.barik at gmail.com> wrote:

> Thanks Linus.
> Sorry, it will not be possible to move to recent kernel.
> How does the mdb gets updated for multicast addresses? Is it learnt on
> basis of packets received from the network? For example, the multicast
> address I use for iperf is I mentioned two scenarios in my
> earlier email. In case of eth0 being the active port on the mbr (multicast
> working scenario), I see br_multicast_new_group() and
> br_multicast_add_group() being called for this IP address moments after mbr
> is up. However in case of wlan0 as the uplink port of mbr, I don't see
> those functions being called.
> I guess for unicast packets, if the entry is not present in fdb, the packet
> is flooded on all other ports and its learnt and added to fdb based on the
> port on which response packet arrives. Is it true for Multicast packets too?
> Regards,
> Saurav
> On Fri, Jul 31, 2015 at 7:27 PM, Linus Lüssing <linus.luessing at c0d3.blue>
> wrote:
> > Hi Saurav,
> >
> > On Fri, Jul 31, 2015 at 03:50:35PM +0530, saurav barik wrote:
> > > I am working on an Access Point device (AP1) running linux kernel 3.0.34
> > on
> > > which my bridge configuration is as follows.
> >
> > There were quite some crucial bugs, I'm not quite sure whether
> > 3.0.34 was actually usuable for multicast snooping.
> >
> > Any chance to try a recent kernel?
> >
> > Cheers, Linus
> >

Multicast forwarding table is built off IGMP messages
When application joins a multicast group an IGMP is sent, and bridge
snoops for that.

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