Code-Memo

Firewalls (iptables, nftables)

Overview

Linux firewalls filter packets using netfilter. Frontends:

• iptables (legacy and nft compatibility layer)
• nftables (modern replacement)

Quick status

iptables (legacy view):

sudo iptables -L -n -v
sudo iptables -S

nftables:

sudo nft list ruleset

Common patterns

Allow SSH (example)

iptables:

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

nft (conceptual):

sudo nft add rule inet filter input tcp dport 22 accept

Persist rules

Depends on distro/tooling:

• nftables service (loads /etc/nftables.conf)
• iptables-persistent (Debian/Ubuntu)
• firewalld/ufw (higher-level managers)

Tips

• Always ensure you have a way back in (console/ILO/serial) before tightening rules on remote machines
• Prefer higher-level tools (ufw/firewalld) if that’s the distro standard

Related

• Firewall configuration