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 5353
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 5353 -j ACCEPT # Ubuntu ufw ufw allow 5353/udp # firewalld firewall-cmd --permanent --add-port=5353/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=5353 action=accept place-before=0 comment="port 5353" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 5353 UDP" -Direction Inbound -Protocol UDP -LocalPort 5353 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 5353 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 5353 -j DROP ufw allow from 203.0.113.0/24 to any port 5353 proto udp /ip firewall filter add chain=input protocol=udp dst-port=5353 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=5353 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 ':5353 ' netstat -ano | findstr :5353 # Windows lsof -i :5353 # macOS