In a rapidly evolving threat landscape, maintaining the security of enterprise networks is critical, with open-source network-based intrusion detection systems (NIDS) playing a vital role in identifying and mitigating threats. The text discusses five notable NIDS: Snort, Suricata, Zeek, OpenWIPS-ng, and Sguil, each offering unique capabilities and benefits. Snort, maintained by Cisco Systems, is notable for its community-driven rule base and versatile detection modes, while Suricata is praised for its real-time capabilities and multithreading. Zeek provides deep network monitoring and operates on the application layer, offering comprehensive protocol analysis. OpenWIPS-ng is specialized for wireless networks, developed by the Aircrack-ng team, and Sguil focuses on efficient data presentation and alert management. These systems support both signature-based and anomaly-based detection methods, though each has its own limitations, such as resource demands or deployment complexity. By understanding these systems' strengths and weaknesses, organizations can better protect their networks from intrusions and data theft.