The set of ports for which a frame with a specific
unicast address will be flooded in the event that it
has not been learned. It also specifies the set of
ports a specific unicast address may be dynamically
learnt on. The portBaseTpFdbTable will have an equivalent
entry with a portBaseTpFdbPort value of '0' until this
address has been learnt, when it will be updated with
the port the address has been seen on. This only
applies to ports that are members of the VLAN, defined
by portBaseVlanCurrentEgressPorts. The default value of
this object is a string of ones of appropriate length.