EPIC Networks

Active and Passive FTP The FTP server may support Active or Passive connections, or both.  In an Active FTP connection, the client opens a port and listens and the server actively connects to it.  In a Passive FTP connection, the server opens a port and listens (passively) and the client connects to it.  You must grant Auto FTP Manager Access to the Internet and to choose the right type of FTP Connection Mode. Most FTP client programs select passive connection mode by default because server administrators prefer it as a safety measure.  Firewalls generally block connections that are "initiated" from the outside.  Using passive mode, the FTP client is "reaching out" to the server to make the connection.  The firewall will allow these outgoing connections, meaning that no special adjustments to firewall settings are required. If you are connecting to the FTP server using Active mode of connection you must set your firewa...

To establish a connection, TCP uses a three-way handshake. Before a client attempts to connect with a server, the server must first bind to and listen at a port to open it up for connections: this is called a passive open. Once the passive open is established, a client may initiate an active open. To establish a connection, the three-way (or 3-step) handshake occurs: 1.            SYN: The active open is performed by the client sending a SYN to the server. The client                         sets the segment's sequence number to a random value A. 2.            SYN-ACK: In response, the server replies with a SYN-ACK. The acknowledgment number                    is set to one more than the received sequence number i.e. A+1, and the sequence          ...