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 4500
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 4500 -j ACCEPT # Ubuntu ufw ufw allow 4500/udp # firewalld firewall-cmd --permanent --add-port=4500/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=4500 action=accept place-before=0 comment="port 4500" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 4500 UDP" -Direction Inbound -Protocol UDP -LocalPort 4500 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 4500 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 4500 -j DROP ufw allow from 203.0.113.0/24 to any port 4500 proto udp /ip firewall filter add chain=input protocol=udp dst-port=4500 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=4500 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 ':4500 ' netstat -ano | findstr :4500 # Windows lsof -i :4500 # macOS