iptables

lumux · 08-22-2003, 06:33 PM

hi all, I am very close to finishing a little router/firewall project I am running, but just need a little help.

I have set up a RH 9 machine with two NIC's one configured on our public "real-ip" network and one on our secure netork.

Now, I have configured a DHCP server for the private network...that is fine.......I found a post describing how to set up iptables to route all traffic through from the secure network out onto the internet, but it is wide open. What I want to know is how do I set up iptables to allow users on the secure network to access the web (ristricted access if possible) and lock down the linux machine with the possible execption of the SSH and HTTP ports (for example).

If anyone good help I would be very greatful

Cheers

Lumux

lumux · 08-22-2003, 06:35 PM

if it helps here is my current iptables config file:

# Generated by iptables-save v1.2.7a on Fri Aug 22 23:41:26 2003
*nat
:PREROUTING ACCEPT [42:2649]
:POSTROUTING ACCEPT [61:3724]
:OUTPUT ACCEPT [61:3724]
-A POSTROUTING -o eth1 -j MASQUERADE
COMMIT
# Completed on Fri Aug 22 23:41:26 2003
# Generated by iptables-save v1.2.7a on Fri Aug 22 23:41:26 2003
*filter
:INPUT ACCEPT [1927:140402]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [2564:188043]
:RH-Lokkit-0-50-INPUT - [0:0]
-A FORWARD -s 192.168.0.0/255.255.255.0 -j ACCEPT
-A FORWARD -d 192.168.0.0/255.255.255.0 -j ACCEPT
-A FORWARD -s ! 192.168.0.0/255.255.255.0 -j DROP
COMMIT
# Completed on Fri Aug 22 23:41:26 2003

Mathieu · 08-22-2003, 07:57 PM

iptables allows you to block ports and track connection.

First of all, you should set the FORWARD chain to drop

Code:

iptables -P FORWARD DROP

and use the following rules to allow related connection.

Code:

iptables -A FORWARD -i eth1 -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT

Also, you should not use Lokkit (RedHat's GUI tool), it is not very good.
Instead, you can learn more about iptables from the documentation and tutorials from netfilter.
http://www.netfilter.org/

Or these GUI tools
http://firestarter.sourceforge.net/
http://www.shorewall.net/
http://www.ipcop.org/
http://www.fwbuilder.org/

lumux · 08-23-2003, 05:39 AM

So all I need to accoplish everything I wrote in my first post can be done with just those three lines?? I find that hard to believe

ppuru · 08-23-2003, 11:30 AM

An alternate method is to use squid proxy.

Mathieu · 08-23-2003, 07:53 PM

Quote:

So all I need to accoplish everything I wrote in my first post can be done with just those three lines?

No.
If you want to block ports, you will need to add more rules.

Looking_Lost · 08-23-2003, 08:28 PM

No offence dude but I gringe when I see the default policy's of aceppt as so many here probably do too.

Mathieu gave you a setup for masquerading which can be added to already dubious rules and ppuru gave you a hint towards access control. Everyone one would love to help you and in the blink of an eye could give you the exact procedures to do what you want to do, but you'll only be back five minutes later asking something else becauses you don't know why what you did works.

As we can see it starts off with how can I share a connection, someone says how to, cool that works, next question how do I open ports etc. and so on....

The old adage Rome wasn't built in a day rings true, no personal slight to you but I've observed so many people demanding without any effort on their own part - relax which so many people forget to do, take one task at a time and before you know it you'll be telling people how to do this and that. The best way to do something right is to do it wrong in the first place.

It's no personal observation on yourself particularly, just a general one, so please don't take offence