fine grained firewall?

Gayn Winters gayn.winters at
Thu Feb 9 08:57:50 PST 2006

> [mailto:owner-freebsd-questions at] On Behalf Of Chuck Swiger
> Sent: Thursday, February 09, 2006 4:30 AM
> To: andrew clarke
> Cc: freebsd-questions at
> Subject: Re: fine grained firewall?
> andrew clarke wrote:
> > Is it possible to configure the FreeBSD firewall to block ports on a
> > per-user or per-executable basis?
> > 
> > eg.
> > 
> > - Block /usr/local/bin/irc from connecting to TCP port 6667
> > 
> > - Block user 'johnsmith' from connecting to TCP port 21
> Yes to users (if the connections originate from the firewall 
> box), no to
> per-executables.  The latter seems useless when "cp irc 
> myirc" is all it would
> take to defeat it.  Frankly, neither option is very useful or 
> would be needed for a good ruleset...

You can block certain types of use, e.g. block irc, by blocking the
outbound ports they use.  You can block user access to some things on
the internet by only allowing a proxy server such access and then having
users authenticate themselves to the proxy server (squid is an example
with a lot of functionality, and it runs on FreeBSD.)  

A lot of people like to block all but a list of applications access to
the Internet. This blocking function is often bundled with Anti-spyware
programs. The thought is that something not on the list might well be
new spyware or other "malware" that has snuck through your security
defenses. These programs need to run on the local workstation, and I
don't know of any for FreeBSD.  While this feature is a pain to manage,
it is probably here to stay as the anti-virus vendors gobble up the
anti-spyware vendors who seem to like it.  Also, don't be surprised if
Microsoft eventually puts this functionality into their base OS.

A lot of firewall vendors are adding non-traditional functionality to
their products. (Anti-virus, anti-spam, proxy server functionality,
outbound policy controls, ...) You can do this with your FreeBSD
firewall as well.  This has the disadvantages of complexity, management,
and performance problems.  

Good luck with your firewall,


Bristol Systems Inc.

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