Firewall Setup

A firewall blocks unwanted traffic before it reaches your applications. On CrazyNode VPS, you have three options: UFW (easiest), firewalld (RHEL-family), or raw iptables/nftables.

UFW (Ubuntu / Debian)

Install UFW

apt install ufw -y

Set default policies

ufw default deny incoming
ufw default allow outgoing

Allow SSH BEFORE enabling

ufw allow 22/tcp

Forgetting this step will lock you out. Use the VNC console to recover.

Allow additional services

ufw allow 80/tcp     # HTTP
ufw allow 443/tcp    # HTTPS

Enable UFW

ufw enable
ufw status verbose

Common UFW commands

ufw allow 3306/tcp                     # allow MySQL
ufw allow from 1.2.3.4                 # allow all from one IP
ufw allow from 1.2.3.4 to any port 22  # allow SSH only from one IP
ufw delete allow 3306/tcp              # remove a rule
ufw reload                             # reload rules
ufw disable                            # turn off (careful)

firewalld (AlmaLinux / Rocky)

systemctl enable --now firewalld
firewall-cmd --permanent --add-service=ssh
firewall-cmd --permanent --add-service=http
firewall-cmd --permanent --add-service=https
firewall-cmd --reload
firewall-cmd --list-all

Network-level filtering

Every CrazyNode VPS also sits behind a network-level filter that blocks obvious DDoS traffic before it reaches your VM. Your local firewall protects against everything else.

Only open ports you actively use. Every open port is a potential attack surface.

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UFW (Ubuntu / Debian)

Common UFW commands

firewalld (AlmaLinux / Rocky)

Network-level filtering

​UFW (Ubuntu / Debian)

​Common UFW commands

​firewalld (AlmaLinux / Rocky)

​Network-level filtering

UFW (Ubuntu / Debian)

Common UFW commands

firewalld (AlmaLinux / Rocky)

Network-level filtering