SNMP traps are not sent even though "Send SNMP traps" is configured in vCenter Server alarm definitions

Products

• VMware vSphere ESXi

Issue/Introduction

An alarm action "Send SNMP traps" is configured in the vSphere Client.
However, SNMP traps are not received by the destination SNMP receiver (Management Server, etc.).

Environment

VMware vCenter Server

Cause

vCenter Server alarm actions utilize the built-in SNMP agent functionality of the vCenter Server.
Enabling the action within an alarm definition is not sufficient by itself; 
if the vCenter Server's global SNMP agent settings (target destination, community string, port, etc.) are not configured, 
traps will not be dispatched.

Resolution

Configure the SNMP receiver settings in the vCenter Server "General" settings.
For detailed steps, please refer to the following Broadcom official documentation:

Configure SNMP Settings for vCenter Server

Note:
After configuration, it is recommended to create a test alarm triggered by an event such as "Virtual Machine Power On" to verify that SNMP traps are successfully dispatched and received.

Additional Information

Please also consider the following points to ensure successful SNMP trap delivery:

- Firewall Port 162 (UDP):
Verify that UDP port 162 is allowed through any firewalls between the vCenter Server Appliance (VCSA) and the monitoring server.

- SNMP Version Mismatch:
Ensure that the SNMP trap version sent by the VCSA (default is v1/v2c) matches the version expected by the monitoring server.

- Monitoring Server Access Control:
Confirm that the monitoring system is configured to accept SNMP traps from the VCSA's IP address (e.g., allow-lists or access control settings).

- Alarm Action Definition:
Double-check the "Alarm Actions" tab of each alarm to ensure the "Send SNMP traps" action is set to trigger on the correct status transitions (e.g., transition from "Warning" to "Critical").

Japanese KB: vCenter Server のアラーム定義で「SNMP トラップを送信」を設定してもトラップが送信されない