GARP Switch Operation
VLAN Operation
2-5
2.4.2.2
Known Unicasts
When a VLAN switch receives a frame with a known MAC address as its destination address, the
action taken by the switch to determine how the frame is transmitted depends on the VLAN, the
VLAN associated FID, and if the port identified to send the frame is enabled to do so.
When a frame is received it is classified into a VLAN. The destination address is looked up in the
FID associated with the VLAN. If a match is found, it is forwarded out the port identified in the
lookup if, and only if, that port is allowed to transmit frames for that VLAN. If a match is not
found, then the frame is flooded out all ports that are allowed to transmit frames belonging to that
VLAN.
For example, assume that a frame is received by the switch depicted in
Figure 2-1
. This frame is a
unicast untagged frame received on Port 3. The frame is then classified for VLAN C. The switch
then makes its forwarding decision by comparing the destination MAC address to its filtering
database. In this case, the MAC address is looked up in the filtering database FID 3, which is
associated with VLAN C and VLAN D. The switch recognizes the destination MAC address of the
frame as being located out Port 4.
Having made the forwarding decision, the switch now examines the Port VLAN List of Port 4 to
determine if it may transmit a frame belonging to VLAN C. If so, the frame is transmitted out Port
4. If Port 4 has not been configured to transmit frames belonging to VLAN C, the frame is
discarded.
2.5
GARP SWITCH OPERATION
Some or all ports on the switch may be activated to operate under the Generic Attribute
Registration Protocol (GARP) applications, GVRP and/or GMRP. For a description of the
protocols and how the frames are handled, refer to the user’s guide of your SmartSwitch device.
