An SNMP device may be configured by its manufacturer to send trap messages which notify the SNMP management station (in this case, SNMP Extension) of certain conditions. Unlike get and set requests, a trap message doesn’t require a request from SNMP Extension. It’s sent by the device automatically when there is an error, a certain level of activity, or other condition. SNMP Extension collects incoming trap messages constantly.
Trap and trap message are used interchangeably.
To receive trap messages with SNMP Management Console, SNMP Management Console's IP address must be included in the trap configuration table of the SNMP agent. Trap configuration is usually separate from general SNMP configuration.
If you configure one but not the other, you may be able to poll the SNMP agent, but receive no trap messages.
The SNMP agent doesn’t expect confirmation for trap messages. If the message doesn’t reach its destination, SNMP Management Console has no way of knowing the message was sent, and the agent has no way of knowing whether a message was received.
Under normal circumstances most of the trap messages do reach their destinations. The limitation of traps comes from the lack of verification capabilities built into the relevant RFC specifications.