The Three-Layer Firewall Model — Why Your Port Is Still Blocked

On Oracle Cloud (and many VPS providers), traffic must pass three independent firewalls in sequence: the cloud Security List, the OS-level firewalld, and the kernel-level iptables. Failing at any one means your port is silently blocked — even if the other two are open.

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⏱ Timestamps:
00:00 Introduction
00:30 Layer 1: Cloud Security List (Oracle/AWS/GCP)
02:00 Layer 2: OS firewall (firewalld)
03:30 Layer 3: Kernel firewall (iptables)
05:00 How traffic passes all three layers
06:30 The most common mistake

#firewall #linux #iptables #firewalld #oraclecloud #devops #networking

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