To enable transparent FTP tunneling, the SOCKS setting in the FTP application needs to be pointed to a localhost listener.
If you are running a real SOCKS proxy on your z/OS system and the localhost port 1080 is already reserved, you can add a second loopback address to your TCPIP profile for the transparent FTP tunneling proxy.
To add the secondary IP address, edit the TCPIP profile on your z/OS system. Under the HOME heading, add the following line:
Make it the second IP address, or put it lower down, because the first address is the machine's default IP address. Follow the procedure shown in ZOS TCPIP Setup. Check that the address is there with the following TSO command: