How will a host (sender) know if Ethernet frame(s) is dropped at receiver side?

Question

when a Ethernet frame is sent from a host (a PC or switch..) and at the receiver side the Ethernet frame is dropped , How will the sender know if it has to resend the same frame.

Answer 1

This is handled (or not) at a higher layer in the protocol stack and switching knows nothing about it.

If you're using UDP or another connectionless protocol, the sender doesn't know about drops at all.

If you're using TCP, each packet sent has a sequence number and the receiver sends back acknowledgements of receipt. The protocol can infer loss of packets from this and resend as needed.

For further explanation, see this wikipedia article on TCP.