Port 161: SNMP
UDP 161 is the port for Simple Network Management Protocol. Never on the internet; default community strings leak full device configuration.
| Service | Simple Network Management Protocol |
|---|---|
| Protocol | UDP |
| Exposure risk | High: do not expose to the internet |
| Secure alternative | SNMPv3 with authentication and encryption |
| Range | Well-known (0–1023): binding needs root/admin on Unix |
Port 161 is UDP-only. UDP has no handshake, so no online checker can reliably tell open from filtered; test with the service's own client.
What port 161 does
Monitoring systems poll routers, switches, printers and servers for counters and status over UDP 161; devices send alerts (traps) to the manager on UDP 162. SNMP v1/v2c authenticate with a plain-text community string such as "public".
Should port 161 be open?
Never on the internet; default community strings leak full device configuration. Where you can, use SNMPv3 with authentication and encryption instead.
Find what's listening on port 161
- Linux:
sudo ss -tulpn | grep :161 - macOS:
sudo lsof -nP -i :161 - Windows:
netstat -ano | findstr :161, then look up the PID in Task Manager.
Open or block it in a firewall
- ufw:
sudo ufw allow 161/udp(ordeny) - firewalld:
sudo firewall-cmd --add-port=161/udp --permanent && sudo firewall-cmd --reload - Windows:
New-NetFirewallRule -DisplayName "Port 161" -Direction Inbound -Protocol UDP -LocalPort 161 -Action Allow
Port assignment per the IANA Service Name and Transport Protocol Port Number Registry. Test several ports at once with the port scanner, or any port with the open port checker.
Questions about port 161
What is port 161 used for?
Is port 161 TCP or UDP?
Is it safe to open port 161?
How do I check if port 161 is open?
ss -ulpn | grep :161 (Linux) or netstat -ano | findstr :161 (Windows).