Intrusion detection system (IDS) is a system designed to detect intrusion on the computer network. IDS can show every time the intrusion comes in the network. IDS implementation can used aplications, such as: ISS Real Secure, Tiger, Snort, and Net Ranger. In this project, the application used is Snort because it is an open-source IDS and easier to study and implement. In addition, Snort has flexible rules and can be implemented in various operating systems. Snort implementation can be done by installing and configuring the Snort and BASE (Basic Analysis and Search Engine) as the Snort interface to the user. At first, download the newest version of Snort and BASE, then install the supporting application such as MySQL, Apache, and ADODB. Finally, configure Snort and BASE from Linux Fedora Core 5 server. The result of Snort implementation is it can alert the system each time an intrusion detected. From the alerts shown in IDS, it is known that the most detected intrusions are generated from TCP protocol. Snort can also give information about the attacks detected, for examples: Trojan horse, worm, or Denial of Service (DoS).