When you configure the ESXi SNMP agent for SNMPv1 and SNMPv2c, the agent supports sending notifications and receiving GET requests.
In SNMPv1 and SNMPv2c, authentication is performed by using community strings. Community strings are namespaces which contain one or more managed objects. This form of authentication does not secure the communication between the SNMP agent and the management system. To secure the SNMP communication in your environment, use SNMPv3.