In this chapter, we will look at common tools and techniques for network monitoring. These techniques can be useful to both alert us to developing problems, and to help troubleshoot existing problems. Network monitoring can be important from a network security standpoint, where it may be useful to detect, log, or even prevent network intrusions.

The following topics are covered in this chapter:

• Checking host reachability
• Displaying a connection route
• Showing open ports
• Listing open connections
• Packet sniffing
• Firewalls and packet filtering