In layer 2 switching, the Ethernet frames should be received from the same port where it was sent, otherwise layer 2 switching or switching loop occurs.

Let me explain this concept with the topology depicted below (Figure -1).

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Figure -1 VLAN load balancing

In the above figure, either Port 1 or Port2 is used to send the traffic, and the same port should be used to receive the traffic. The switches use MAC addresses to process the Ethernet frames. Read more