Data connection setup

The following two FTP protocol commands are available for setting up the data connection with IPv6 addresses:

• EPRT: PORT command extended by IPv6 capability

• EPSV: PASV command extended by IPv6 capability

The following two modes are available for setting up data connections:

• Active mode

• Passive mode

Active mode

Connection setup takes place with an active child and passive client. The child is notified of its own connection endpoint with the aid of the following commands:

• PORT command if the home address is an
  IPv4 address (IPv4-MAPPED address).

• EPRT command if the home address is an IPv6 address.

PORT a1, a2, a3, a4, p1, p2 EPRT |2|a|p|

ai, i = 1,..,4: IPv4 address; pi, i = 1, 2: port number 2: IPv6 protocol, a: IPv6 address in colon notation, p: port number

Passive mode

Passive mode is selected using the client command passive (see the manual “interNet Services User Guide”).

The data connection is set up with a passive child and active client. The child sends its IPv4 address including the port number (PASV) or just its port number (EPSV), which the client then combines with the server’s IPv6 address known from the control connection.

This process is started by one of the two following commands sent by the client:

• PASV command if the server’s IP address for the control connection is an IPv4-MAPPED address.

• EPSV command if the server’s IP address for the control connection is an IPv6 address.

227 Entering Passive Mode (a1, a2, a3, a4, p1, p2)	ai, i = 1,..,4: IPv4 address; pi, i = 1, 2: port number (response to PASV)
229 Entering Extended Passive Mode EPRT (|||p|)	p: port number (response to EPSV)

Passive mode is now the default setting in many client implementations and is used to go from a LAN onto the Internet via a firewall. Such firewalls often prevent active connection setup to the user’s own LAN.