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SELinux

This is a special Security feature built into most Linux distributions. Lets take RHEL for example. If permissive or enforcing mode is enabled, an SELinux policy must be selected to determine which programs are governed by SELinux and which are run in unconfined space. The SELinux policy sets what programs are protected under SELinux. The default policy, called the targeted policy, in Red Hat Enterprise Linux is designed to protect the system without being intrusive to the users.

Ethereal

One of my favourite tools for watching incomming and outgoing data packs on my network. Ethereal can track more than 100 packet types ( representing different protocols ). On Redhat Linux 9, this packages is pre-instaled and can be started up by typing # ethereal & from the command line. The primary function of Ethereal is to take snapshot of the packets comming across your network interface and display that data in the Ethereal Window.

You can filter the filter the data based on the variety of filter primitives. When the capture is done, you can step through and sort the data based on the valuesin different columns. Optionally, you can save the captured data to a file to study the data at a later time.

Firewall

The Firewall settings for most networks, operating systems or services go a long way in determining how safe your network could actually turn out. Setting your firewall to medium is a good start and should help counter intruders to a certain degree. Nevertheless, most times other services on your network could be affected by your firewall settings so you'll need to know your onions if you are to get the best filtering service from your firewall settings.

Open SHH

This is a secure shell service which can make life easy for Network administrators. It uses a file encription technique which secures data packs sent accross networks and this tool is usually shiped on most Linux distros by default. Open Shh is another open source tool which requires an intermediate knowledge of common Unix commands to get the best out of it, but overall is lovely to try.

Getting Updates

It's always usefull to check for updates on any security tools you choose to use especially if they are open source tools. With the fast development of many open source applications, it's very usefull to check for patches or bugs discovered by developers (usually in the community of users) so as to enhance security features of that particular tool or application. This also helps to keep you informed on the latest advancement of security breaches and possible loop holes you could encountern using such application.

Other Network tools

There are so many tools to assist system administrators for a safe day to day running of your Nework, some i can recommend include LanAlyzer, Sniffer, Microsoft Network Monitor, Wireshark, Snoop and more...