This managed object is a filter used for identify the target from which
the MAC addresses are learned in macTable. The target could be:
1: Subtending port 1
2: Subtending port 2
3: Uplink port 1
4: Uplink port 2
5: All of the four uplink ports
6: All ports in the system
IfIndex is used for identifying subscriber ports (e.g. 300 means all ports in slot 3
and 301 means port 1 in slot 3).