Firewall

Overview The Linux firewall has evolved from ipfwadm → ipchains → iptables → nftables. All are based on the Netfilter framework, but the higher-level syntax and management approach have continuously improved. This article starts from the Netfilter architecture and dives into iptables’ five chains and four tables, nftables’ advantages and usage, NAT/port forwarding, connection tracking, and production performance optimization. Netfilter Framework Architecture Overview Netfilter is a packet processing framework in the Linux kernel that implements packet filtering, address translation, connection tracking, and other functions by mounting hooks at key positions in the kernel network stack....

Introduction A default Linux server installation exposes a far larger attack surface than most realize: unnecessary RPM packages, open network services, permissive SSH configurations, and inactive audit systems. Security hardening is not a one-time operation but a full lifecycle checklist from installation to runtime. This article follows the CIS Benchmark framework to organize hardening essentials, with directly executable configurations for each step. System Minimal Installation Principles Package Management Trimming The core principle of minimal installation: install only what you need, not what you might need....