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Re: Recommendations for a simple firewall please


My machines, all windows, access the net (browsing and download pop email) thru one Linux machine acts as a gateway and it has an ISDN/PPP connection.    The Gateway runs KDM.  The windows machines use telnet, Xfree86 to access Linux.

I use the following script.  Its simple.  Its appears secure.  And I think I even know what it does :-)  I built it after reading various random "how-tos" on iptables, so I cliam no originality for it.

I took this approach cause the myriad of possible firewalls just were too complicated to properly understand, and I wanted something that made sense to me.

Of course I might have it all wrong ....


-----------------------------------------cut here-------------------------------------------

# Build a NAT Firewall

# ippp0 interface connects us via ISDN to the Internet
# eth0 connects us to the internal network of mostly windows PCs


# Flush all the rules in filter and nat tables

   iptables --flush
   iptables --table nat --flush

# Delete all chains that are not in default filter and nat table

   iptables --delete-chain
   iptables --table nat --delete-chain


# stop ALL incoming connections on ippp0
#       NEW connections we don't want.
#       INVALID stuff goes no further

   iptables -A INPUT -m state --state NEW,INVALID -i ippp0 -j DROP

# Hide internal LAN via NAT

   iptables --table nat --append POSTROUTING --out-interface ippp0 -j MASQUERADE

# allow forwarding from local Ethernet

   iptables --append FORWARD --in-interface eth0 -j ACCEPT


At 09:31 PM 12/02/2003, Tony Sequeira wrote:
Hi all,

I am running 2 machines with Debian Woody, one has X, the
other not.

They both have their own dial up access to the internet,
and are on an internal network (192.168.0.)

I have installed ferm and ipmenu on the non X machine, but
am having difficulty setting up a firewall.

The X machine has uses firestarter, but not quite as things
should be, Firestarter starts on a boot up, but typically
starts so restrictively, that I cannot download my email or
surf the web.  I have to stop and reconfigure firestarter
after every bootup.  The documenattion says that a single
configuration file should be reusable, but I cannot find
where to place it.

I spent a weekend playing with ferm/ipmenu on the other
machine, and got in a hell of a mess.

Documentation is minimal at best.  I don't have the
grounding to set these things automatically.

I would like a firewall that springs into action when I
dial up my ISP, and goes down when I disconnect.

If someone can suggest the best tool(s) to use for such a
requirement and point me at a reasonably verbose HOWTO, I
would be grateful.



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