Re: PORT or PASV mode of IIS 4.0's FTP

[Adam Prato <sirsyko () MERGIOO ISHIBOO COM>]

On Wed, Aug 02, 2000 at 06:30:01PM -0400, C. K. Lung wrote:
> What is the "mode" of a FTP server running on MS IIS 4.0 w/sp6a?  Is it "normal/standard", "passive" or both?  Can it 
> be configured by the administrator?
>
> How about the ftp client comes Solaris?  Is "normal", passive or both?
>
> The ftp client is trying to "get" 15,000 1-K files from the IIS's FTP server, the connection is killed by FW-1 after 
> it got 100 files.  The fw-log shows that when the client's "source port" hit a "pre-defined service (port) in the 
> rulebase, the connection is dropped.  CP explained that FW-1 thought that it was a security violation.
>
> Talked to many people at work, no-one could offer any explanation.
>
> Any pointers are appreciated.
>
> Thanks,
>
> CLUNG

wether its "passive" or "active" is a function of the client, not the server.
A server *could* be configured to not accept passive, or active, or both.

Please investigate how ftp works for more information. Reading either Kit Knox
or Hobbit's FTP white papers should give you more insight into the issues
regarding ftp. But in a nutshell:

passive ftp = the following commands

PASV
<transfer command>

active ftp = the following commands

PORT A,B,C,D,X,Y
<transfer command>

The difference between the PASV and the PORT command is: who is the "client"
socket and who is the "server" scoket. In the case of PASV, the FTP SERVER
becomes the "server socket". This means that the ftp client connects to the
ftp server, and the ftp server sends the data. In the case of the PORT command
the FTP CLIENT becomes the "server socket". This means that the ftp server
connects to the ftp client, then the ftp server sends the data.

<transfer command> is either STOR, RECV, NLST, and others.

If *none* of this makes sense, search altavista for the papers written by
Kit Knox or Hobbit, or even peruse the FTP protocol specification. Or even
better yet, invest some money in the W. Richard Stevens books on network
programming (not directed specifically at you, directed at the learning
community).

<ss>