[geeks] News server access
joshua d boyd
geeks at sunhelp.org
Tue Aug 14 22:06:05 CDT 2001
On Tue, Aug 14, 2001 at 09:42:18PM -0400, Ken Hansen wrote:
> IIRC, FTP starts on one port, then takes the conversation (file exchange) to
> another, random port - freeing up the original port for (more connections? -
> drawing a blank)
Speaking from the experience of once writing my own FTP client, I'd like
to clarify here.
FTP starts on one port, and keeps that port open. This is the control
port. Just telnet to the ftp port on a server, and you can talk to it in
Then, when the client starts a download, the client tells the server what
port to open. So the clients says something like:
and the server initiates a connection to port 31337 on the client machine.
BTW, while it isn't really supported these days, in the spec it is
possible for a client to have one server send files directly to another
without all the packets passing through it. So, a 56k link can initial a
transfer between two T1s at T1 speed.
I don't have the RFC number handy though since I'm not at my machine. FTP
is interesting though.
Joshua D. Boyd
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