I am going to take a wild guess at how she "memorized" it, because I do not
think she memorized it, nor copied and pasted it from somewhere. She
probably derived it, and possibly cut and paste it from
there. At least that is what I would do.
Not sure if you said the last line in jest, but here is my take on just in
case you were serious.
My guess is all she needed to know is, the theory. Yes, if you learn the
theory, holy moly, you do not have to memorize every little detail. Why?
Because, she only needs to know 3 basic theories.
Passive FTP
Active FTP
Basic TCP/IP (yes, the one thing that everyone seems to put on their resume,
but knows squat about).
Basic TCP/IP handles the concept of the different ports. FTP being a
befangled protocol from heck, will have the listening port either be on the
client or server. This of course, just creates "wonderful" scenarios for
firewalls that do not have some kind of "proxy" like feature. I leave that
as an exercise for the reader.
I hope this post does not come off as trying to downplay Priscilla. I am
not trying to downplay Priscilla, I think she rocks the casbah! :) Just
saying that, a little bit of theory goes a long long long long way if you
know how to apply it. And that, in my opinion, is infinitely better than
any amount of raw memorization. (same as the teach someone to fish instead
of giving him fish statement). It is unfortunate that theory has been
downplayed as the "oh I know the theory, but I do not know how it reallly
works" (that just reeks of an oxymoron to me in so many ways).
Read some RFCs on how the FTP protocol is meant to work and the two
different forms of how FTP will transfer data. Also, learn how basic TCP/IP
works. SYN, SYN+ACK, ACK, RST, FINs, ephermal ports, well-
known ports, that should be as clear to you as your native language if you
know how TCP/IP works. I did not mean to be offensive, I mean to be as
helpful as possible! Good luck!
> Way off topic:
>
> 1. Priscilla mentions ephemeral ports at the end of this post. I just
> saw "Scanners" this weekend and the drug they use to give people wacky
> telepathic powers was "ephemerol". Apparently it gives you the ability
> to make people's heads explode, just like networking can at times!
>
> 2. Priscilla, please tell me you cut and paste that stuff from
> somewhere and don't just reel it off from memory (e.g. the 10-step FTP
> process below). If you do reel it off from memory, do you use some
> herbal memory supplement or something?
>
> -John
>
>
> ""Priscilla Oppenheimer"" wrote in message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Although I can't answer your question, I can tell you how FTP works
> > and maybe that will help. I can believe that it has problems in your
> situation!
> > ;-)
> >
> > FTP does not use both TCP and UDP. It does, however, open multiple
> > TCP connections.
> >
> > Assuming you are using Active (non-passive, aka PORT mode), here's
> > what happens:
> >
> > 1. The client sends a TCP SYN to the well-known FTP control port
> > (port 21) on the server. The client uses an ephemeral (short-lived,
> > not well-known, greater than 1024) port as its source port. 2. The
> > server sends the client a SYN ACK from port 21 to the ephemeral
> port
> > on the client.
> > 3. The client sends an ACK. The client uses this connection to send
> > FTP commands and the server uses this connection to send FTP
> > replies. 4. When the user requests a directory listing or initiates
> > the sending or receiving of a file, the client software sends a PORT
> > command that
> includes
> > an ephemeral port number that the client wishes the server to use
> > when opening the data connection. The PORT command also includes an
> > IP address, which is usually the client's own IP address, although
> > FTP also supports a third-party mode where a client can tell a
> > server to send a file to a different host. (Third-party mode is
> > rarely used.) 5. The server sends a SYN from port 20 to the client's
> > ephemeral port number, which was provided to the server in the
> > client's PORT command. 6. The client sends a SYN ACK from its
> > ephemeral port to port 20. 7. The server sends an ACK. 8. The host
> > that is sending data uses this new connection to send the data in
> > TCP segments, which the other host ACKs. (With some commands, such
> > as STOR, the client sends data. With other commands, such as RETR,
> > the server sends data.) 9. After the data transfer is complete, the
> > host sending data closes the data connection with a FIN, which the
> > other host ACKs. The other host also sends its own FIN, which the
> > sending host ACKs. 10. The client can send more commands on the
> > control connection, which may cause additional data connections to
> > be opened and then closed. At some point, when the user is finished,
> > the client closes the control connection with a FIN. The server ACKs
> > the client's FIN. The server also sends its
> own
> > FIN, which the client ACKs.
> >
> > Notice that an additional command (DIR, in your example) opens
> > another
> data
> > connection. (In Active mode, these data connections come from the
> > server's port 20.)
> >
> > Now, if you're using Passive mode, the client opens the data
> > connection, from an ephemeral port to an ephemeral port on the
> > server. Here are the steps:
> >
> > 1. The client sends a TCP SYN to the well-known FTP control port
> > (port 21) on the server. The client uses an ephemeral port as the
> > source port. 2. The server sends the client a SYN ACK from port 21
> > to the ephemeral
> port
> > on the client.
> > 3. The client sends an ACK. The client uses this connection to send
> > FTP commands and the server uses the connection to send FTP replies.
> > 4. When the user requests a directory listing or initiates the
> > sending or receiving of a file, the client software sends a PASV
> > command to the
> server
> > indicating the desire to enter passive mode.
> > 5. The server replies. The reply includes the IP address of the
> > server and an ephemeral port number that the client should use when
> > opening the connection for data transfer. 6. The client sends a SYN
> > from a client-selected ephemeral port to the server's ephemeral port
> > number, which was provided to the client in the reply to the
> > client's PASV command. 7. The server sends a SYN ACK from its
> > ephemeral port to the client's ephemeral port. 8. The client sends
> > an ACK. 9. The host that is sending data uses this new connection to
> > send the data in TCP segments, which the other host ACKs. (With some
> > commands, such as STOR, the client sends data. With other commands,
> > such as RETR, the server sends data.) 10. After the data transfer is
> > complete, the host sending data closes the data connection with a
> > FIN, which the other host ACKs. The other host also sends its own
> > FIN, which the sending host ACKs. 11. The client can send more
> > commands on the control session, which may cause additional data
> > connections to be opened and then closed. At some point, when the
> > user is finished, the client closes the control connection with a
> > FIN. The server ACKs the client's FIN. The server also sends its
> own
> > FIN, which the client ACKs.
> >
> >
> > The gist of your problem is these multiple connections that happen.
> > I assume that HTTP works fine. That's probably because it opens only
> > one connection.
> >
> > So, is there some more advanced configuration you can do to make FTP
> > work? That's the question.....
> >
> > As far as your idea of fixing the problem with a static route, I'm
> > afraid that won't work because static routes don't let you specify a
> > port number. Would policy routing work? It's going to be tricky,
> > though, because of those ephemeral ports.
> >
> > Maybe you could just pull one of the connections when you do FTP!
> > ;-)
> >
> > HTH
> >
> > Priscilla
> >
> >
> > ________________________
> >
> > Priscilla Oppenheimer
> > http://www.priscilla.com
-Carroll Kong
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