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6.1.1 Unicast Switching
This section describes VLAN classification, learning, filtering, and forwarding for unicast switching.
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• VLAN Classification
- If the frame is untagged, the switch classifies the frame into the default VLAN for the incoming
port.
- If the frame is tagged, the switch uses the tagged VLAN ID to identify the broadcast domain of the
frame.
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• Learning
After VLAN classification, the switch checks the <source MAC address, VLAN> pair in the
address table to see whether this pair is known.
- If unknown, the switch adds this pair to the address table.
- If known, the switch checks the pair for an incorrect Port ID. If the PID associated with the pair in
the address table is different from the receiving port, the switch modifies the PID in the address
table.
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• Filtering
After learning the address, the switch checks:
- If the source or destination port is not in the forwarding state. (For example, if it is in blocking state
or has been disabled.)
- If the source or destination MAC address is to be filtered.
- If the source PID is the same as the destination PID.
If any of these conditions are met, the switch drops the received frame. Otherwise, it continues with the
forwarding process as described below.
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• Forwarding
During the forwarding process, the switch checks whether the <destination MAC address,
VLAN> pair is unknown.
- If unknown, the switch floods the received frame to all ports in the VLAN, excluding the source
port.
- If known, the switch forwards the received frame to the port associated with the pair. At the same
time, the switch decides whether a VLAN tag needs to be added to or stripped from the frame,
depending on the VLAN tagged/untagged configuration and VLAN ID for the output port.
• Aging— the switch performs the aging process for the <MAC addresses, VLAN> pair in the MAC
address table. Once a pair is aged out, the address table is modified.
WGS3 Layer 3 Switch User's Manual
When the switch receives a frame, it classifies the frame in one of two ways:
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