Is it safe to open
Management interfaces give full control of the system. Make them reachable only from an admin network or VPN, change default credentials and keep the software patched.
How to open port 161
Open to everyone
# Linux iptables iptables -A INPUT -p udp --dport 161 -j ACCEPT # Ubuntu ufw ufw allow 161/udp # firewalld firewall-cmd --permanent --add-port=161/udp && firewall-cmd --reload # MikroTik /ip firewall filter add chain=input protocol=udp dst-port=161 action=accept place-before=0 comment="port 161" # Windows (PowerShell) New-NetFirewallRule -DisplayName "Port 161 UDP" -Direction Inbound -Protocol UDP -LocalPort 161 -Action Allow
Only for your addresses
# allow only one address or network (replace 203.0.113.0/24) iptables -A INPUT -p udp --dport 161 -s 203.0.113.0/24 -j ACCEPT iptables -A INPUT -p udp --dport 161 -j DROP ufw allow from 203.0.113.0/24 to any port 161 proto udp /ip firewall filter add chain=input protocol=udp dst-port=161 src-address=203.0.113.0/24 action=accept /ip firewall filter add chain=input protocol=udp dst-port=161 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 ':161 ' netstat -ano | findstr :161 # Windows lsof -i :161 # macOS