Is it safe to open
Infrastructure services (DNS, NTP, DHCP, routing) should answer only the networks they serve. Open resolvers and time servers get abused for DDoS amplification.
How to open port 67
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 67 -j ACCEPT # Ubuntu ufw ufw allow 67/udp # firewalld firewall-cmd --permanent --add-port=67/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=67 action=accept place-before=0 comment="port 67" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 67 UDP" -Direction Inbound -Protocol UDP -LocalPort 67 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 67 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 67 -j DROP ufw allow from 203.0.113.0/24 to any port 67 proto udp /ip firewall filter add chain=input protocol=udp dst-port=67 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=67 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 ':67 ' netstat -ano | findstr :67 # Windows lsof -i :67 # macOS