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Configuring Workgroups Using LCM
5-3
It is also possible to overlap workgroups. Figure 5-2 shows how overlapping
ports can communicate with ports in both Workgroups. For example, Workgroup
Alpha 3-7 and Workgroup Omega 7-9. In this example, four workgroups would
be created, Alpha, Omega, the default, and a superset workgroup containing all
ports in Alpha and Omega. In this case ports 3-6 would be limited to
communicating with ports within Alpha. Ports 8 and 9 would be limited to
communicating with ports in Omega. However, port 7 can communicate with
ports within both Alpha and Omega.
Figure 5-2. Traffic Overlapping Within Workgroups
The system is able to do this because the system places additional entries in the
database that allow the two-way communication. In the previous example, when
a packet is received on port 7, its source MAC address is stored in the database
with a Workgroup identifier. In this case it is the identifier of the superset
(0x06e). When a device on ports 3-6 or 8 and 9 try to send a packet to that MAC
address, it has no way of combining the destination MAC address with the
Workgroup identifier for port 7 (0x06e). For example, if the packet is received on
port 3, the packet is labeled with the Workgroup identifier for Workgroup Alpha
(0x065). A lookup will be done on the MAC address and Workgroup ID pair
(0x065). In this case, it would not be found and the packet would be flooded to
all members of Workgroup Alpha. The two devices would be able to
communicate, but only because of the flooding.
To avoid flooding, the system places additional entries into the database. When
the first packet is received on port 7, three entries are placed into the database.
One for the superset (0x06e), one for Alpha (0x065), and one for Omega
(0x066). By placing three entries, when the responding device sends a packet to
Ports 3, 4, 5, 6, 7
Ports 3 through 9
Workgroup Superset
Workgroup Omega
Workgroup Alpha
Ports 1, 2, and 10 through 27
Workgroup Default
7 8, 9