Further reading
Vendors explain firewalls:
Cisco: https://www.cisco.com/c/en_uk/products/security/firewalls/what-is-a-firewall.html
Fortinet: https://www.fortinet.com/resources/cyberglossary/firewall.html
Checkpoint: https://www.checkpoint.com/definitions/what-is-firewall/
Palo Alto Networks: https://blog.fuelusergroup.org/from-first-gen-to-next-gen-the-evolution-of-the-firewall
OpenLearn - Introduction to cyber security
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