Internet wasn't meant the exact replica of real world, with its threats and dangers projecting in cyberspace. The very nature of many protocols and services doesn't assume there could be denial-of-service and other kinds of attacks, nor deliberate misuse of the resources. Astaro Internet security mentions several basic ideas in their post How to protect your network from cyber-attacks.
It is said that there are three measures network administrators can take to avoid the types of network attacks that plague government websites in many countries nowadays. The three areas to focus on are network based mitigation, host based mitigation and proactive measures.
Network based mitigation:
Host based mitigation:
Proactive measures:
For those with the knowhow, it would be possible to “fight back” with programs that can neutralize the threat. This method is used mostly by networks that are under constant attack such as government sites.
However, one could add that the prevention is in most cases much more productive than defense and counterattacks. Most attackers do use the brute force or known vulnerabilities exploits at random; if the problem isn't handled as soon as possible, the amount and thoroughness of attacks may grow, especially if the site or service, or whatever is being under attack is of much importance.
In other words, the optimal network security strategy is to use network monitoring and early prevention to detect possible threats, thus taking measures quickly, in as automated manner as possible. It also has social effect: if network prevents major assaults quickly and takes little or no damage, its reputation can repel most of probable attackers (not all the cyber-crimes are committed with the single purpose of deliberately harming the target).