Avoiding bridge flood of multicast when L2 switch is used
Subsystems (2)
netdev experts,
When there is a L2 switch underneath the network interface a flooding of multicast at the bridge interface results in one copy of this going through each of the slave resulting in multiple multicast packets reaching the underlying switch. L2 switch also duplicates the multicast packet on each egress port as done in software bridge. This is undesirable as it reduces the available bandwidth to half when multicast packets are involved.
Is there something that can be done to avoid software bridge flooding mulicast through a ip command or similar or to be done in the network driver? I have a TODO item to add dsa support in our netcp driver. If this is already solved by dsa, I can handle it as part of this work.
Thanks in advance for your response!
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Murali Karicheri Linux Kernel, Keystone
Quoted 5 lines
netdev experts,
When there is a L2 switch underneath the network interface a flooding of multicast at the bridge interface results in one copy of this going through each of the slave resulting in multiple multicast packets reaching the underlying switch.
Yes, this is something Florian, Vivien and i have discussed. We don't yet see a way around it. Neither the Marvell or Broadcast switches have a mechanism to say: Send this frame out of this list of interfaces. All we can do is send it out a single interface. Even if we could direct a single frame out multiple interfaces, we still have the problem of how to teach the bridge about this, in a clean and elegant fashion.
Overall, this seems like a hard problem. Since it is a hard problem, implementing IGMP snooping first would make sense. Don't forward the packet out a port unless you know there is somebody interested in it. The swichdev parts of IGMP snooping are in place, we just need to continue them down into DSA.
Quoted 3 lines
L2 switch also duplicates the multicast packet on each egress port as done in software bridge. This is undesirable as it reduces the available bandwidth to half when multicast packets are involved.
Once you have a DSA driver, the switch will not do this replication. So you will gain something there.
Andrew