if you want to know what is snort - Snort is a popular and powerful packet sniffer program

you can download at http://www.snort.org

Snort can function in a more sophisticated role such as an Intrusion detection system (IDS). an IDS is a program that monitors network traffic for suspicious activity and alerts the appropriate administrator to warning signs. so basically an IDS is a packet sniffer with the ability to recognize activity patterns that indicate an attack in your network is under way.