What you will learn
- Write iptables/nftables rules
- Understand cloud security groups
- Apply default-deny
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The basics, in plain English
A firewall is a gatekeeper that decides which network traffic is allowed in or out. It is the most basic way to keep unwanted connections away from your machines.
- Firewall
- A filter that allows or blocks network traffic based on rules you set.
- Rule
- A single instruction like “allow web traffic on port 443, block everything else”.
- Inbound vs outbound
- Inbound is traffic coming to your machine; outbound is traffic leaving it.
- Security group
- A cloud firewall attached to a server, controlling what can reach it.
- Default deny
- The safe habit of blocking everything first, then only opening what you truly need.
01
Default deny
Good firewall posture denies everything, then opens only what is needed. Cloud security groups are stateful allow-lists on instances.
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