12.8. Network Security

Making your server secure is a complex task requiring you to control the operation of the entire network. The least you have to do is monitor all communication channels to know, which of them are being used.

The easiest way of doing this is to use the nmap utility. It allows the ping command to be executed for the entire network, thus revealing , which servers and computers are currently accessible. If some computer has not responded, you have to investigate the causes of this. Perhaps, this is only because of a power loss or unscheduled reboot. But it may also be caused by a successful DoS attack, and you should be the first one to know about this.

The nmap utility is extremely handy for a one-time check but inconvenient for constant monitoring. I prefer using the CyD NET Utils ( www.cydsoft.com ) utility for this purpose. The utility, however, has a serious shortcoming: It only works under Windows.

Unfortunately, despite my extensive search on the Internet, I have not been able to find any comparable Linux program and I assume there is none. Thus, until one is developed, the nmap utility remains your only choice for network monitoring under Linux. Despite its inconvenience, it is better than nothing.