Hi Andrew,

Andrew Lunn [off-list ref] writes:

SWITCHDEV_ATTR_ID_PORT_PARENT_ID is used by the software bridge when
determining which ports to flood a packet out. If the packet
originated from a switch, it assumes the switch has already flooded
the packet out the switches ports, so the bridge should not flood the
packet itself out switch ports. Ports on the same switch are expected
to return the same parent ID when SWITCHDEV_ATTR_ID_PORT_PARENT_ID is
called.

DSA gets this wrong with clusters of switches. As far as the software
bridge is concerned, the cluster is all one switch. A packet from any
switch in the cluster can be assumed to of been flooded as needed out
all ports of the cluster, not just the switch it originated
from. Hence all ports of a cluster should return the same parent. The
old implementation did not, each switch in the cluster had its own ID.

Also wrong was that the ID was not unique if multiple DSA instances
are in operation.

Use the MAC address of the master interface as the parent ID. This is
the same for all switches in a cluster, and should be unique if there
are multiple clusters.

That is not correct. Support for multiple CPU ports is coming and in
this case, you can have two CPU host interfaces wired to two switch
ports of the same tree. So two different master MAC addresses.

Only the tree ID assigned by DSA core is unique to a given tree.


Thanks,

        Vivien