Which defensive technique involves the server sending a wrong syn+ack to the client, so the client sends and rst packet notifying the server of an error? this makes the server think the client request is legitimate?

 Which defensive technique involves the server sending a wrong syn+ack to the client, so the client sends and RST packet notifying the server of an error? this makes the server think the client request is legitimate? Answer is an RST cookie

Answer the important painting of the baptism of the christ, leonardo painted the kneeling angel and some of the background for this;