Re: [SLUG] Forwarding internal FTP connections

[Ken Yap <ken@xxxxxxxxxx>]

>Ah ok - I was always a little hazy on what passive mode did exactly. So
>it just means that the remote server won't make a return connection to
>send data.

Well it's not so much the direction of data transfer as who waits for a
data connection. Traditional mode goes like this:

	> dir
	-> port a,b,c,d,e,f (client says I'm at this address and port)
	<- (server says ok)
	(server connects to client and data transfer happens)

Passive mode goes like this:

	> dir
	-> pasv (client says you tell me where to connect)
	<- (server replies with address and port)
	(client connects to server and data transfer happens)

Obviously traditional mode is no use if the client sends a private
untranslated address. Note that the address is sent in the control
connection and a translator has to reach in and modify the address.

You can see all this by enabling debug in ftp.