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associated with the pair in the address table is different from the receiving port,
the switch modifies the PID in the address table.
• 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.
• 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.
4.1.2.Multicast Switching For multicast switching, the switch checks whether the received frame is a Bridge
Protocol Data Unit (BPDU). If a BPDU is received, the switch forwards the frame for
processing by the Spanning Tree Protocol. Otherwise, the switch performs the following
processes:
• VLAN classification—same as for unicast switching (chapter 4 “Unicast Switching”).
• Learning—same as for unicast switching (chapter 4 “Unicast Switching”).
• Filtering—after learning, the switch checks the same filtering criteria used for unicast
switching (chapter 4 “Unicast Switching”), except there is no destination MAC
address to check.
• Forwarding—the switch floods the received multicast frame to all ports within the
VLAN, excluding the source port. 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—same as for unicast switching (chapter 4 “Unicast Switching”).
4.1.3.Spanning Tree Algorithm The Spanning Tree Algorithm (that is, the STA-configuration algorithm as outlined in