RE: FTP Problem under USB connection
From: Corey Burke [MS] (coreyb_at_online.microsoft.com)
Date: 03/21/05
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Date: Mon, 21 Mar 2005 21:37:53 GMT
When you connect to remote hosts over the USB sync cable, you're using a
feature called desktop passthrough (DTPT). DTPT only supports outgoing TCP
connections. No incoming and no UDP traffic.
The FTP protocol has the client connect to the server on the command
channel (port 21). Since you're the client this is an outgoing TCP
connection and DTPT reroutes it through the desktop the way you'd expect.
However when data needs to be transferred like a file download or upload, a
second data connection is established. By default, the FTP protocol
specifies that the server should connect back to the client on a addr/port
endpoint specified in a PORT command. But this is an incoming connection
to the client and is not permitted by DTPT (for security reasons).
Instead you should use FTP's passive mode (PASV) in which the client makes
the data connection to the server instead of the other way around. For
Wininet you can specify that passive mode should be used by setting the
INTERNET_FLAG_PASSIVE flag in the dwFlags field of your call to the
InternetConnect function.
-Corey
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