OK Thomas, I´ll clarify. I have one ISA server SP1 in integrated mode. 2 NICs are installed in this server - 1 for the external network (the Internet) and 1 for the internal network (192.168.x.x). The XP Pro client is installed on the internal network. I am not using DHCP. It is on the XP Pro client an application exist which has to be accessible by external users (Internet) and according to the application maker, TCP ports 4262, 4711 and UDP port 4672 have to be forwarded (the incoming direction) to the client since users on the Internet will otherwise not see the client. They will only see the servers IP. I think I am clear about that I have to create some types of packet filters but I am not sure on how to configure these. Thanks, Johny Lundgren