🧱 IPTables, Demystified — Linux Firewall Fundamentals for Blue Teams

If you’re in SysAdmin, DevSecOps, Cloud, SOC, or Network Security, this is core knowledge for traffic control, segmentation, and incident response on Linux hosts.

🧠 What the Guide Breaks Down

1️⃣ Firewall Architecture 101
External vs internal firewalls and where IPTables fits
Stateful inspection & connection tracking in plain language

2️⃣ How IPTables Is Structured
Tables: filter, nat, mangle, raw, security
Chains: INPUT, OUTPUT, FORWARD, etc.
How a packet actually travels through the kernel routing path

3️⃣ Building Real Rules (Not Just Copy-Paste)
Why a default DROP policy is your safest baseline
Letting only ESTABLISHED and RELATED traffic through
Handling loopback, DHCP, SSH, FTP/TFTP the right way
From zero to “basic firewall deployed & persistent”

4️⃣ Advanced Topics for Practitioners
Connection tracking with conntrack
Passive vs active FTP nuances
Tuning modules and limits (e.g. nf_conntrack_max, timeouts, NAT helpers)

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