We currently VPN into our network through a SonicWall Pro 330 and able to connect to our internal network and produce an active IPSec tunnel. We are currently in the process of converting our servers instead of using the Sonicwall as its gateway, but instead going out through a newly installed ISA server that sits on our DMZ as its external port and a second NIC internal with a fixed NAT IP address. This is where the problem arises, the servers that are still currently using the Sonicwall as its gateway are able to be seen through the VPN tunnel (pinged). But those that have been converted to use the ISA server as its gateway, even though its IP address is one of the Internal NAT IP addresses given out by the Sonicwall DHCP, they are unable to be seen through the VPN tunnel.