Force ProFTPD to listen on only one IP

It's not quite as clean as the socket binding under Apache but the principle works something like this.

1. In Standalone mode, to listen on the primary IP of a host use the SocketBindTight directive.

   In "/etc/proftpd.conf":

   SocketBindTight                 on
   

2. To listen on a interfaces which are not the primary host interface, use the SocketBindTight directive, place your server configuration in a block and use "Port 0" for the main host configuration and and "Port 21" inside the VirtualHost block.
   Port                            0
SocketBindTight                 on
<VirtualHost xxx.xxx.xxx.xxx>
        Port 21
        DefaultRoot             ~
        AllowOverwrite          on
        Umask                   002
</VirtualHost>