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I have some systems running on Ubuntu in the private IP range 192.168.2.0-255 . These systems are connected to a switch and the switch is connected to the ISP's modem.

Neither the switch nor the modem support firewall options. I don't have any firewall device and I'm not willing to individually configure firewalls on all the systems (via gui/iptables).

Is it possible to make an Ubuntu system into something like a software firewall, so that all the traffic/packets sent to or from the WAN(internet) would be allowed/denied based on its firewall rules?

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sudo ufw enable –  Anonymous Nov 17 '11 at 20:52
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3 Answers 3

up vote 3 down vote accepted

AFAIK almost every distribution can be set as a firewall. And also there are some distro specifically built for this purpose such as zentyal, clearos etc. 'zentyal' is based on Ubuntu while 'clearos' is based on Centos.

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I"ll give a try of them –  user3215 Feb 24 '11 at 1:28
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Firestarter Install Firestarter

Firestarter is an Open Source visual firewall program. The software aims to combine ease of use with powerful features, therefore serving both Linux desktop users and system administrators.

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Firestarter features

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* Suitable for use on desktops, servers and gateways
* Real-time firewall event monitor shows intrusion attempts as they happen
* Enables Internet connection sharing, optionally with DHCP service for the clients
* Allows you to define both inbound and outbound access policy
* Open or stealth ports, shaping your firewalling with just a few mouse clicks
* Enable port forwarding for your local network in just seconds
* Option to whitelist or blacklist traffic
* Real time firewall events view
* View active network connections, including any traffic routed through the firewall
* Advanced Linux kernel tuning features provide protection from flooding, broadcasting and spoofing
* Support for tuning ICMP parameters to stop Denial of Service (DoS) attacks
* Support for tuning ToS parameters to improve services for connected client computers
* Ability to hook up user defined scripts or rulesets before or after firewall activation
* Supports Linux Kernels 2.4 and 2.6
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Is it possible to manage or administer remote computer firewall setting rules with firestarter? –  user3215 Feb 24 '11 at 1:27
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You can install Gufw it's an easy to use free software to configure the internal Ubuntu's firewall (Netfilter).

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Please note that this will ONLY be effective if the computer sits between the modem and the switch. You can't just have it hanging off the switch like all the other boxes and expect it to be able to block packets heading towards them. #obvious-but-worth-stating –  Jeremy Oct 14 '10 at 7:24
    
Also, you will have to check if netfilter sets the ip_forwarding option in the kernel. If not, please see this: ducea.com/2006/08/01/how-to-enable-ip-forwarding-in-linux –  Jeremy Oct 14 '10 at 7:25
    
One more thing. Not all software firewalls are equal, depending on what you want to be doing. It's worth looking into the differences between iptables, netfilter and pf. –  Jeremy Oct 14 '10 at 7:26
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Is it like that installing Gufw on a single system I can handle the firewall settings on remote systems which are on the same network?. –  user3215 Oct 14 '10 at 8:39
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