Currently what is the best Firewall & Internet security for Ubuntu?
Ubuntu has an inbuilt firewall caled ufw
The graphical version for it is gufw. Search in the Ubuntu Software Center you will find it
Ufw is installed by default and is one of the strongest firewalls ever
See this Ubuntu Documentation for Firewalls
Regarding an Antivirus software, you dont need one because linux rarely catches a virus.
There are hardly any linux viruses
If you insist on having one for windows files on linux,
Then install Clamav found in the Ubuntu Software Center and the gui frontend for it is clamtk also found in the Ubuntu Software Center.
Check these Ubuntu documentations for more info
Also see this
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?
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.
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.
You can use Firestarter on your...
... desktop or laptop. Our philosophy of simplicity has made Firestarter the most widely used Linux desktop firewall software available today.
... server. Firestarter can be installed onto individual servers and managed graphically over SSH or using the shell.
... gateway or dedicated firewall. Firestarter will set up Internet connection sharing for you with a minimum of fuss. Want DHCP for the clients? Sure you could configure it yourself, but we know you never get around to doing it, with Firestarter it only takes one click.
* Open Source software, available free of charge
* User friendly, easy to use, graphical interface
* A wizard walks you through setting up your firewall on your first time
* 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
* Translations available for many languages (38 languages as of November 2004)
You can install Gufw it's an easy to use free software to configure the internal Ubuntu's firewall (Netfilter).