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Old 08-06-2002, 03:42 PM   #1
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Angry I give up!


I've tried my own ideas and it's failed miserably - I think I managed to over complicate things. So from the beginning...

I have an ADSL router that is ONLY capable of working with the network.

I have a Linux box with RH7.3 on it two NICS

What I want is to set the linux box up as firewall to my ADSL connection and to ensure that all traffic entering / leaving my network goes through this machine.

I then have two other machines that are running windows and these need to be able to access the internet.

Can someone point me in the right direction regarding topology and routing information. PLEASE!

Old 08-06-2002, 03:56 PM   #2
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Is it a router or a modem?
What is the make and model?
Is your dsl PPPoE?
Do you want the dual homed box outside the router?(not possiible if it's a modem.)
Now if everything inside the adsl router/modem is privately addressed (ie on the 192.168.x.x network) do you need a firewall. These machines aren't reachable from the internet.

Is your router capable of any fw? does it do NAT? Will it proxy?
Old 08-06-2002, 04:04 PM   #3
Registered: Feb 2002
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You may do it this way:
network           ------------ router ---------- ADSL
(Windows machines)
                     (eth1)               (eth0)
Small explanation:
* Network of Windows machines is using 192.168.2.x adresses.
* RH machine has two nics. One, connected to Windows machines is The second one, connected to ADSL is
* RH has ipchains or iptables masqerade installed.
Old 08-06-2002, 05:10 PM   #4
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Thanks. SamYan first...

It's a ZyXEL Prestige 600 Router

I THINK my dsl is PPPoE

My original thoughts were for a dual homed box.

No the oruter can do FW. It does do NAT and No I don't think it will proxy.


My intial implementation was along those lines. I had 2 nics one addressed as (eth1) and the other (eth0)
The router is
I had Ip forwarding turned on
I had the default gateway of the windows machines set to
Whilst the Linux box was quite happy to browse the web the windoze machines weren't.

I tried changing the subnet mask on both the router and eth0 to be this had the effect that I could see outbound (from the win machines) IP packets (ethereal) on the eth0 network but no packets were being returned - I was testing using ping.

I would like to get this working as eventually I would like to host an internet visible server outside of my protected windoze network.
Old 08-06-2002, 11:01 PM   #5
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Is it a router or ADSL modem? I have a couple of these - they are ADSL modems. You can turn your linux box into a hardware firewall with smoothwall
Old 08-07-2002, 02:04 AM   #6
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The main part of the problem is, I think, that the ADSL router has NAT, but only for 192.168.1.x. It may not mask other IPs. So you can 2 ways:
1) eth0 =, eth1 =, Windows boxes - other 192.168.1.x IPs. In this situaltion you need to set up route carefully.
2) Something easier(?) to configure - NAT on RH box. In this case you'll have 2 NATs, but it's OK. You can get one of simple NAT scripts from (you'll need a firewall, most scripts have both NAT and firewall).


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