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From: Andre Oppermann <oppermann@pipeline.ch>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Listening at a socket
Date: Thu, 19 Jun 1997 22:10:21 +0200
Organization: Internet Business Solutions Ltd. (AG)
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Message-ID: <33A9922D.7844@pipeline.ch>
References: <5oblqi$4re@ui-gate.utell.co.uk>
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Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:43165
Hi Brian
It uses the different port numbers of the FTP processes on
the FTP-client machine:
FTP-Client X --------> FTP-Server Y
ftp1 on port 12345 --
|--> port 21
ftp2 on port 23456 --
Every outgoing connection has a unique port number.
> This *has* to be a dumb question, but can anyone tell me
> how an OS, once it's received a packet for a given port
> X, can distinguish which process of all the processes that
> are using that port should get that packet.
>
> For example, if I run an ftp server, I have my ftpd
> listening on *.21. If I currently have 2 established
> connections from the same remote machine, I'll have two
> additional ftpd processes running (forked from the first).
> When a packet is received from the other machine destined
> for port 21, how does the OS decide which process to deliver
> the packet to ?
--
Andre Oppermann
CEO / Geschaeftsfuehrer
Internet Business Solutions Ltd. (AG)
Hardstrasse 235, 8005 Zurich, Switzerland
Fon +41 1 277 75 75 / Fax +41 1 277 75 77
http://www.pipeline.ch ibs@pipeline.ch