I’m running an FTP server using IIS 4.0 on NT4 server sp6a. This server is not multi-homed. This server is connected to the internet through a WIN2K server using NAT. The NAT server is configured to route requests coming in on port 21 to the FTP server. Most remote clients have no problem accessing this server. Other remote clients can connect but are unable to open a data connection.
I have captured the packets from successfull connections and failures. On the failures, the last FTP command issued by the client is ‘PASV’. The server responds ‘227 entering passive mode’ and sets a port. After that the server does not recieve anymore ftp packets from the client, and the client returns a can’t open data connection error.
However these same clients can access other ftp servers such as ftp.microsoft.com.
Any help would be greatly appreciated.