Fix Port Not Opening in Firewall

Verify Port is Actually Closed

nmap -p PORT YOUR_IP
nc -zv YOUR_IP PORT

sudo netstat -tlnp | grep :PORT
sudo ss -tlnp | grep :PORT

For UFW (Ubuntu/Debian)

sudo ufw status verbose
sudo ufw allow PORT/tcp
sudo ufw status numbered
sudo ufw delete RULE_NUMBER
sudo ufw reload

Common UFW Issues

sudo ufw default allow
# Not recommended

# Rule order matters (first match wins)

For firewalld (CentOS/RHEL)

sudo firewall-cmd --get-active-zones
sudo firewall-cmd --permanent --zone=public --add-port=PORT/tcp
sudo firewall-cmd --reload
sudo firewall-cmd --list-all
sudo firewall-cmd --zone=public --query-port=PORT/tcp

For iptables

sudo iptables -L -n -v --line-numbers
sudo iptables -A INPUT -p tcp --dport PORT -j ACCEPT
sudo iptables-save > /etc/iptables/rules.v4

Check Service Binding

sudo lsof -i :PORT

Cloud Firewall

Check VPS provider firewall rules (applied before OS firewall).

Test Firewall Issue

sudo ufw disable
sudo systemctl stop firewalld
sudo iptables -P INPUT ACCEPT
sudo iptables -F

If port works after disabling firewall, configuration issue is confirmed.