Port 161 — UDP
SNMP monitoring and polling of network devices.
What is port 161 used for?
Monitoring and device queries.
Transport protocol
UDP
Security precautions
Prefer SNMPv3 with appropriate authentication and privacy settings. Avoid default SNMPv1/v2c community strings.
Should we open this port in the firewall?
Allow this port only when a required service uses it. Apply least privilege: restrict authorized sources, destinations and interfaces, and log connections where appropriate.
How do I check this port?
Test-NetConnection -Port tests TCP, not UDP. Query the device with an authorized SNMP client and inspect its response, monitoring logs and a packet capture.
Capture UDP 161 during a real application exchange and verify the request and response. UDP has no TCP-style handshake; a missing reply to a generic probe does not prove that the port is closed.
Port-to-service mappings are common conventions. Applications can use a different configured port; confirm the actual service and transport.