| Packet analyzers are a necessity for any network administrator. Sniffers copy each packet on their local segment and display it to the user for analysis. A good packet analyzer can determine everything that is traversing the network. Sniffers gather information that is necessary in fixing network problems and defining what happens during a security attack. Sniffers allow network administrators to view network traffic, see what type of traffic is allowed on that network segment, and determine whether rules on the packet filtering router and firewall are blocking disallowed traffic. After an attack is in progress, it is too late to use a sniffer.