A switch (S6730-H48X6C-V2) forwards each frame that enters an interface over a transmission medium. The basic function of a switch is to forward frames.
A switch processes frames in three ways: flooding, forwarding, and discarding.
- Flooding: The switch forwards the frames received from an interface to all other interfaces.
- Forwarding: The switch forwards the frames received from an interface to another interface.
- Discarding: The switch discards the frames received from an interface.
Flooding
As shown in this figure:
- Scenario 1: Host 1 wants to access host 2 and sends a unicast frame to the switch. After receiving the unicast frame, the switch searches the MAC address table for the destination MAC address of the frame. If the destination MAC address does not exist in the table, the switch floods the frame.
- Scenario 2: Host 1 wants to access host 2 but does not know the MAC address of host 2. Host 1 sends an ARP Request packet, which is a broadcast frame to the switch. The switch then floods the broadcast frame.
Forwarding
As shown in this figure:
- host 1 wants to access host 2 and sends a unicast frame to the switch. After receiving the unicast frame, the switch finds the corresponding entry in the MAC address table and forwards the frame in point-to-point mode.
- If a unicast frame enters a switch interface over a transmission medium, the switch searches the MAC address table for the destination MAC address of the frame. If the corresponding entry is found in the MAC address table, the switch checks whether the interface number corresponding to the destination MAC address is the number of the interface through which the frame enters the switch over the transmission medium. If not, the switch forwards the frame to the interface corresponding to the destination MAC address of the frame in the MAC address table. The frame is then sent out from this interface.
Discarding
As shown in this figure:
- Host 1 wants to access host 2 and sends a unicast frame to switch 1. After receiving the unicast frame, switch 1 searches the MAC address table for the destination MAC address of the frame. If the destination MAC address does not exist in the table, switch 1 floods the frame.
- After receiving the frame, switch 2 finds that the interface corresponding to the destination MAC address is the interface that receives the frame. In this case, switch 2 discards the frame.
- If a unicast frame enters a switch interface over a transmission medium, the switch searches the MAC address table for the destination MAC address of the frame. If the corresponding entry is found in the MAC address table, the switch checks whether the interface number corresponding to the destination MAC address in the MAC address table is the number of the interface through which the frame enters the switch over the transmission medium. If yes, the switch discards the frame.
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