Is it safe to open
VPN ports are meant to be open. Use modern protocols (WireGuard, IKEv2), strong keys, and keep the VPN software up to date.
How to open port 500
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 500 -j ACCEPT # Ubuntu ufw ufw allow 500/udp # firewalld firewall-cmd --permanent --add-port=500/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=500 action=accept place-before=0 comment="port 500" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 500 UDP" -Direction Inbound -Protocol UDP -LocalPort 500 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 500 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 500 -j DROP ufw allow from 203.0.113.0/24 to any port 500 proto udp /ip firewall filter add chain=input protocol=udp dst-port=500 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=500 action=drop
If the server is behind a router, you also need a port forward (dst-nat). Behind ISP CGNAT (100.64.0.0/10 on the WAN) forwarding will not help: you need a public IP or a VPN.
What is listening
Check on the server
# what listens on the port ss -lntup | grep ':500 ' netstat -ano | findstr :500 # Windows lsof -i :500 # macOS