[Bridge] Are multicast Ethernet frames supported in Linux bridge?

[Martin T]

Stephen,

thanks! Once I disabled multicast snooping under
/sys/devices/virtual/net/br0/bridge/multicast_snooping, then bridge
started to forward multicast Ethernet frames.


Martin

On 3/25/15, Stephen Hemminger <stephen at networkplumber.org> wrote:
> On Wed, 25 Mar 2015 11:01:57 +0200
> Martin T <m4rtntns at gmail.com> wrote:
>
>> Hi,
>>
>> I have a network topology where in "Dell PE860" runs a Linux
>> virtual-switch br0:
>>
>> http://s24.postimg.org/j1un2gs9h/virtual_bridge.png
>>
>> Now if I send an Ethernet frame to broadcast address from "IBM
>> ThinkCentre":
>>
>> 17:10:23.569021 00:a1:ff:01:02:05 > ff:ff:ff:ff:ff:ff, ethertype IPv4
>> (0x0800), length 34: 127.0.0.1 > 127.0.0.1:  ip-proto-0 0
>>
>> ..then I see this frame in both virtual-machines as I should. If I
>> send an Ethernet frame to MAC address which is not known in br0 MAC
>> address table, then the br0 also behaves correctly and floods the
>> frame to all ports expect to one where the frame came in(eth1 in this
>> example). However, if I send a multicast frame from "IBM ThinkCentre":
>>
>> 17:17:05.513283 00:a1:ff:01:02:05 > 01:33:44:55:66:77, ethertype IPv4
>> (0x0800), length 34: 127.0.0.1 > 127.0.0.1:  ip-proto-0 0
>>
>> ..then for some reason Linux virtual-switch does not flood it to all
>> the ports(except the one where the frame came in from). Why is that
>> so? I would expect that switch handles multicast frames exactly like
>> broadcast frames.
>>
>>
>> thanks,
>> Martin
>
> Linux bridge does IGMP snooping (by default).
> Therefore you need an application that uses IGMP advertisements
> or manually disable this via sysfs.
>