Re: Unable to FTP to i from desktop

[Booth Martin <booth@xxxxxxxxxxxx>]

Consider using http://filezilla-project.org/

I use this regularly and it talks nicely with an AS/400.

Simon Coulter wrote:
> On 05/05/2009, at 5:51 AM, Vinay Gavankar wrote:
>
>   
> > I get 'Invalid command' message when I do pasv. (pasv is not listed  
> > as a
> > valid command when I do 'help' at the ftp prompt).
> >     
>
> Then get a better FTP client. My guess is you are using the pathetic  
> client supplied with WinDOS which does not support PASV (at least not  
> on any release up to and including XP). Although it satisfies the  
> minimum implementation described in Section 5.1 of RFC 959 it fails to  
> satisfy the required minimum implementation as described in Section  
> 4.1.2.13 of RFC 1123.
>
> As Scott K. has explained on numerous occasions FTP requires two  
> ports: one for Control and one for Data. CD and a number of other FTP  
> commands send both the command and the data across the Control port  
> but file transfers send the data across the Data port.
>
> Servers that correctly implement the FTP RFC will use the port  
> immediately adjacent to (and lower than) the control port for the  
> default data port. Hence, for most servers port 21 is the control port  
> and port 20 is the data port. However, it seems that many servers  
> don't do this and just grab an ephemeral port for the data port.
>
> Clients that correctly implement the FTP RFC will use the client  
> control port for the default data port and compliant servers will  
> understand this behaviour. Clients that do this generally do not have  
> a problem with Firewalls** because the same port is used for control  
> and data. The only issue with using the default data port is the TCP  
> delay before reusing a closed port but a good client will handle this.
>
> Good clients will support PORT to change the default data port. Better  
> (and currently compliant) clients will support PASV to inform the  
> server to expect an incoming data connexion.
>
> Properly compliant clients, such as the OS/400 FTP client (at least as  
> far as PORT and PASV are concerned), allow you to disable PORT and  
> PASV which will force the default data port to be used. Most clients  
> either do not allow disabling or only allow PORT to be disabled.
>
> So you need a client that will either allow the default data port to  
> be used or supports PASV. The WinDOS FTP client does neither.
>
> **Note that a Firewall configured to allow outgoing connexions but  
> reject incoming connexions will still break the FTP default data port  
> because the default FTP behaviour is for the server to connect back to  
> the client.
>
> Regards,
> Simon Coulter.
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