Data port assignment

Your selection is applicable only when clients log in using IPv4 addresses.

When an FTP client logs in to a server, a connect request flows from the client to the server to establish a control connection. When a client wants to transfer data, for example with a get, a different connection, referred to as a data connection, must be established to handle the transfer. Unlike the control connection, there are multiple ways a data connection can be established. The server can initiate the connect request or the client can initiate the connect request, depending on the level of FTP RFC support.

There are differences between the RFC 1579 and the RFC 2428 protocols.

The use of the EPSV command may be useful if you are encrypting data on the control connection, for example with Transport Layer Security (TLS). If your data passes through a firewall using Network Address Translation (NAT), the firewall is not be able to interpret the IP address on the PASV reply, which may cause problems. By using the EPSV command and reply, no IP address is sent, rather the client and server already understand the address.