Lynda - Protect Your Network with Open-Source Software (repost)

Network protection is vital to organizations big and small, but it doesn't have to be an expensive proposition. Learn how to protect your network with open-source tools, and do it completely FREE. Jungwoo Ryoo shows how to set up firewalls, investigate network traffic with a packet analyzer, detect threats and malicious activity with an intrusion-detection system, and enable network logging and monitoring. Start here for a low-cost route to a more secure network.