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Date:	Fri, 2 Oct 1998 11:44:43 PDT
From:	"Gregory W. Smith" <gsmith@well.com >
Reply-To:	scoug-programming@scoug.com
To:	< "scoug-programming@scoug.com" > scoug-programming@scoug.com >
Subject:	SCOUG-Programming: FTP server - po

Content Type: text/plain

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On Fri, 2 Oct 1998 11:06:56 PDT, Emerson, Tom # GPS-MDI wrote:
>On Friday, October 02, 1998 7:09 AM, Peter Skye
>[SMTP:attmail!internet!peterskye.com!pskye] wrote:
>> Hi Greg,
>>
>> Gregory W. Smith wrote:
>> >
>> > If the FTP server gets a request from joe@abc.net on port 20, it
>> > spawns child process "A" that has the established connection on port
>> > 20. The child process then opens a data connection with joe@abc.net
>on
>> > port 21 and then does all of the file transfers. The parent process
>> > then closes its connection on port 20 and then re-opens port 20 to
>> > listen for the next user.
>>
>> So the Port 20 "handle" (or whatever) is passed to A-joe@abc.net?
>> Doesn't that jeopardize the integrity of the system? Couldn't Joe,
>> being a malevolent sort of person, try to read some Port 20 packets and
>> totally flummox the FTP server?
>>
>> Or are the ports irrelevant because the processes are using sockets? A
>> socket is basically a handle for a specific IP address and port number.
>
>> Is it the handle (the socket) that's passed from the server to the
>child
>> process?
>
>OK, I see it's time for "networking 101" to begin session:
>
>The PHRASE OF THE DAY: A Purple Snake Takes No Dead Prisoners
>
>This stands for the seven layers of the "7-layer OSI networking model":
>
> pplication
>

resentation
> ession
> ransport
> etwork
> ata-link
>

hysical

I learned this as "All Protocols Should Talk Nice Like Padlipski.
(Nothing like using the mneumonic to plug your own book.) Anway, I
have put a networking introduction from Rutgers up on my Web page for
those who are interested. You can get it as:

<http://www.well.com/user/gsmith/intro.pdf>

You will need the Acrobat Reader to view the file. You can get the
reader as a free download from Adobe at:

<http://www.adobe.com/prodindex/acrobat/readstep.html>

(I distilled the PostScript to PDF myself with Aladdin GhostScript.
The original is from the January 1994 InfoMagic Standards CD-ROM.)

===============================================================
Gregory W. Smith (WD9GAY) gsmith@well.com
finger gsmith@well.com for PGP public key
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