An IDS (intrusion detection system) monitors network traffic and alerts administrators of potential malicious activity. An IPS (intrusion prevention system) also monitors traffic but can block malicious traffic. Both connect passively to a network to analyze traffic. Common IDS/IPS tools include Snort, Suricata, and Cisco. Access control lists on routers can block traffic but only based on IP and port. Firewalls can also block traffic but provide additional capabilities like application inspection and can enforce access policies. Both block traffic but firewalls offer more robust security features.