WebsiteintermediateFree
sans.org
Unknown
Site of the SANS Institute, a leading cybersecurity training and certification provider. It offers course catalogs and GIAC certifications, plus an extensive library of security resources—white papers, research, reading room, webcasts, blogs, and incident response/forensics guidance.
More resources on Network Security
WebsiteFree
Cisco Networking Academy
Free self-paced network security courses
WebsiteFree
Krebs on Security
Real-world network security news and analysis
WebsiteFree
HackTheBox
Free network pentesting challenges
CourseFree
Practical Ethical Hacking
Learn ethical hacking skills with TCM Security's practical network security course! Hands-on labs included.
CourseFree
Network Security
Learn network security essentials with this Cisco course. Master concepts and skills to protect networks from threats.
WebsiteFree
OWASP
Open Web Application Security Project - free security resources