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  • From: Matrix Mole <matrixm AT sdf.lonestar.org>
  • To: baslinux AT lists.ibiblio.org
  • Subject: Firewalling (was Re: [BL] Modem questions)
  • Date: Wed, 9 Jun 2004 04:50:35 +0000 (UTC)

On Mon, 7 Jun 2004, James Miller wrote:

Let us know how you get along with both these projects: I'd like to know
if ppp does what you need and works more predictably than diald. It would
also be interesting to know what you end up using for a firewall.

Well, I took a look at the Linux-FIREWALL-How-To and it does a pretty good job of describing the way to setup Linux as a firewall system. From what I've read in it, Linux can be used as a firewall almost out of the box. You may ahve to recompile kernel (for ip-forwarding/ipMasqueradeing) but that type of stuff is still in my "Need to learn" category still.

Essentially though, (very basic breakdown coming here): You set up your network so that all traffic goes into the linux box. Then, the linux box is setup to not allow any traffic to go out to the internet. The linux box has two seperate IP addresses, one for inside the network (192.168.0.5 for example) and then the one for the internet (63.64.296.124 for example). If you have ipforwarding on, then anypacket that is suppsoed to go out to the internet, will instead be sent to the linux box, who will then forward it to the internet properly (this is my understanding of the concept at least, basically Linux with ipforwarding operates identical to Windows ICS). I may be totally off here, it seems more like I'm describing NAT as opposed to firewalling, since theres really nothing to do with port blocking at all in this setup. Anyway, if you want ot prevent internet traffic from getting to the local side of the linux box, then you have ipforwarding turned off, and install a proxy server on linux. So, I opbviouslly have a lot to learn still, but from this basic setup, if you have any server daemons running on the linux box, they would be wide open to the internet as well as your local network (telnet, ftp, etc). This doesn't seem like a very secure setup to try and use BL for without installing the shdadow.tgz package. So, I still have a lot to read, if for nothing else than the secure methods of blocking out and controlling the what data is allowed to connect to the linux box on what ports.

Just what I've learned so far. The Firewall How To can be found at tldp.org/docs.html along with quite a bit else obviously.

--
Matrix Mole
matrixm AT sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org
Running BasicLinux error free since May 15, 2004




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