The Deltanji routine %vc830 implements an FTP server that Beyond Compare connects to for diffing objects, change requests, components etc. In situations where there is a requirement to encrypt data as it travels between the server and the client, FTPS (FTP over SSL) can be used.

Deltanji support both active and passive FTP connection modes. See this article for details about the differences, but in a nutshell, here is how the the FTP(S) protocol uses its command and data channels. The server port numbers below assume %vc830 is started on port 21.

Active FTP :
     command : client >1023 -> server 21
     data    : client >1023 <- server 20

Passive FTP :
     command : client >1023 -> server 21
     data    : client >1024 -> server >1023

A quick summary of the pros and cons of active vs. passive modes:

• Active FTP is beneficial to the FTP server admin, but detrimental to the client side admin. The FTP server attempts to make connections to random high ports on the client, which might be blocked by a firewall on the client side.
• Passive FTP is beneficial to the client, but detrimental to the FTP server admin. The client will initiate both connections to the server, but one of them will be to a random high port, which might be blocked by a firewall on the server side.