3Com corebuilder 3500 Implementation Manual page 243

If MAC address 00-80-3e-12-34-56 is learned on port 3 and port 3
belongs to port group 1, it has a port group bit mask for port group 1
inserted into the port group mask table that is associated with the MAC
address in the bridge address table. The mask is 32 bits long and
contains:
32 bits
0 0 0 0 0 0 0 0 0 0 0 0 0 0
32
If MAC address 00-80-3e-aa-aa-aa is learned on port 5 and port 5
belongs to port group 2, it has a port group bit mask for port group 2
inserted into the port group mask table that is associated with the MAC
address in the bridge address table. The mask is 32 bits long and
contains:
32 bits
0 0 0 0 0 0 0 0 0 0 0 0 0 0
32
When you use the source or destination port group mask (SPGM and
DPGM) commands in your filter, you are referencing the port mask of the
source port and the port mask of the destination port, respectively. You
can use these commands to verify if the source and destination addresses
of the packets are members of the same port group to implement your
filtering algorithm.
A frame is received (unicast/multicast/broadcast) on the source port. The
source port group mask (SPGM) is found in the table of port group
masks, using the received port as the index. The destination port group
mask (DPGM) is found after the bridge determines whether the port is to
be forwarded (known DA unicast) or flooded (unknown DA unicast, or
multicast, or broadcast).
For forwarded frames, the single SPGM and DPGM are used in the packet
filter.
For flooded frames, each pair of SPGM and DPGM are individually
processed. The filter is repeated for each pair of Source and Destination
ports.
Using Port Groups in Custom Packet Filters
0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0
243
0 0 0 1
2 1
0 0 1 0
2 1