From owner-freebsd-net  Sat Mar 20 12:37:37 1999
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Date: Sun, 21 Mar 1999 07:07:13 +1030
From: Ian West <ian@apdata.com.au>
Organization: Applied Data Control
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To: Matthew Hagerty <matthew@venux.net>
Cc: freebsd-net@freebsd.org
Subject: Re: Proxy, NATd, what's the dirrerence?
References: <4.1.19990320133441.00a322e0@mail.venux.net>
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Matthew Hagerty wrote:
> 
> Greetings,
> 
> Sorry if this is a little off topic, but can someone explain to me the
> difference between a proxy server and a NATd server?  I am having a hard
> time finding a clear explanation.
> 
> Thank you,
> Matthew
> 
> To Unsubscribe: send mail to majordomo@FreeBSD.org
> with "unsubscribe freebsd-net" in the body of the message

In real basic terms, a proxy reads data, and retransmits it on a
seperate conenction, nat just rewrites the header info with the
translated addresses, so it is possible to pass evil options through,
even though the addresses are not visible from 'outside'.

A proxy is generally (although not necessarily) an independant program
dedicated to filtering the particular type of data it is applied to.
This can be generalised a bit for tcp streams, but udp, icmp, and ftp
need to be handled a bit more carefully. (ftp because of the data
connection is independant of the control connection). Often proxys will
do quite a lot more filtering as well, such as checking line lengths for
smtp for example. (Or url's for http etc etc..)

Hope this helps,
Regards,
Ian


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