1. What's active mode and passive modea. FTP has two ports to control:Port 20 is for data transferPort 21 is for control or establish TCP connectionb. The process of active connectionNote: C represents Client and S represents ServerS opens port 20 and 21C connects to port 21 of S with a random port, this port can be between 1024 and 65536, it sends port+x to server at the same time to specify C(X)->S(21)When S receives the command, it will sends back ACK, S(21)->C(X)S will set up a connection between its port 20 and client's X+1, S(20)->C(X+1)C responds with an ACK,C(X+1)->S(20)c. ...