Computer Networking
Firewalls & VPNs
Rules that allow or deny traffic by address, port and protocol; stateful inspection; encrypted tunnels.
The question this module answers · A ping fails but the service works. What is a firewall actually blocking?
Firewalls
▶ interactive
A firewall is an ordered rule list evaluated against each packet’s addresses, ports and protocol — stateful ones remember which connections you started so replies get in — and a silent drop looks completely different on the wire from nothing listening.
VPNs and Tunnels
▶ interactive
A VPN wraps whole IP packets inside encrypted packets, adds a virtual interface and a route that sends chosen destinations through it — and every byte of wrapper is a byte of MTU your packets no longer have.