Is it safe to open
File-sharing protocols are not designed for the internet: they leak data and spread ransomware. Keep them inside the LAN and give remote users a VPN or an HTTPS-based service instead.
How to open port 138
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 138 -j ACCEPT # Ubuntu ufw ufw allow 138/udp # firewalld firewall-cmd --permanent --add-port=138/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=138 action=accept place-before=0 comment="port 138" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 138 UDP" -Direction Inbound -Protocol UDP -LocalPort 138 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 138 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 138 -j DROP ufw allow from 203.0.113.0/24 to any port 138 proto udp /ip firewall filter add chain=input protocol=udp dst-port=138 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=138 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 ':138 ' netstat -ano | findstr :138 # Windows lsof -i :138 # macOS