Great Circle Associates Firewalls
(December 1995)
 

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Subject: Proxy v. Packet Filter
From: rex @ staff . cs . su . oz . au (Rex di Bona)
Date: Fri, 22 Dec 1995 08:55:04 +1000
To: firewalls @ GreatCircle . COM
Reply-to: rex @ cs . su . oz . au

> Can someone tell me exactly what a Proxy can do 
> that a good packet filtering firewall cannot do?
> 
> _Pete Morrissey
> _Syracuse University

As an example - my mail proxy parses the mail from/to lines and the
envelope header looking for known 'sendmail' bug chars, and other
illegal/unwanted characters. (Not that I actually run sendmail - ugh!).
This would be difficult (impossible?) with a packet filter. The
difference is that a proxy looks at the data in the stream, whereas a
filter only looks at source and dest.  (Ignoring hybrid mixtures
here).

					Rex.


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