Implement router filters. This will lessen your exposure to certain DoS attacks. - If such filters are available for your system, install patches to guard against TCP SYN flooding.
Disable any unused or inessential network service. This can Limit the ability of an attacker to take
advantage of these services to execute a DoS attack.
Enable quota systems on your OS if they are available.
Observe your system's performance and establish baselines for ordinary activity. Use the baseline to
gauge unusual levels of disk activity, central processing unit (CPO) usage or network traffic.
Routinely examine your physical security with regard to your current needs.
Use Tripwire or a similar tool to detect changes in configuration information or other files
Invest in and maintain "hot spares" - machines that can be placed into service quickly if a similar
machine is disabled.
Invest in redundant and fault-tolerant network configurations.
Establish and maintain regular backup schedules and policies, particularly for important configuration information.
Establish and maintain appropriate password policies, especially access to highly privileged accounts
such as Unix root or Microsoft Windows NT Administrator.