How bound/tie a Network service/port to a particular Alias IP Addr only

[Declan Mc Kay]

Hi is it possible to tie down a Network Service to a specific IP Addr (Alias IP)??
If so how..?
I have a 3rd part Appl which has it's own build-in FTP Servicer daemon,,,however, what I would like to do is tie tcp/21 to the NIC's physical IP Address for the HP's own ftpd and then also tie same port tcp/21 to the 3rd Party s/w FTP server daemon. So when I ftp to the Phy Adr I get the HP's FTP server and when I FTP to the Alias IP I get the 3rd s/w FTP service....?
Maybe this isn't at all possibe,,,but is what I would like to achieve. Anyone have any ideas?