Firewall

Executive Summary Networking baseline = reliable, secure, predictable connectivity with proper tuning for your infrastructure. Why networking configuration matters: Most production outages trace back to network issues: misconfigured firewall blocking traffic, exhausted connection tables, or timeouts set too aggressively. Proper networking prevents these disasters. Real-world disasters prevented by good networking: 1. Firewall accidentally blocks production traffic: Problem: Engineer adds SSH rule, accidentally sets policy to "drop all" Result: Website goes down, SSH also blocked (can't fix it remotely) Prevention: Test firewall rules with policy "accept" first, then switch to "drop" 2. Connection tracking table exhausted: …

Executive Summary A security baseline is the foundation: OS-hardened, patched, with restricted access and audit trails. This guide covers minimal-install servers with hardened SSH, firewall (default-deny), LSM enforcement, least-privilege sudo, audit logging, and systemd hardening. Goal: Reduce attack surface, detect breaches, and enforce privilege boundaries. 1. Minimal Install & Patching Minimal Install What it is: Install only required packages (base + SSH + monitoring agent) No GUI, X11, unnecessary daemons Reduces vulnerabilities (fewer packages = fewer CVEs) Install steps (Ubuntu/Debian): …