Allow what is needed, keep the block

Articles

• ping — check whether packets reach a host — The ping command sends ICMP echo requests to a host and prints replies, latency and loss — the first network check.
• ss — sockets and ports — Shows who is listening on ports and which connections are open; a netstat replacement, faster with many connections.
• curl — HTTP requests from the console — curl sends HTTP and HTTPS requests from the console: status code, headers, the whole exchange, certificate checks.
• conntrack — connection tracking — The kernel's connection table — what NAT/firewall see, overflow, debugging.
• Firewall — nftables / ufw — A mechanism filtering network traffic according to specified conditions and actions.