TUT:Configuring snmptrapd to receive SNMPv3 notifications

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SNMPv3 background

Before you can begin to understand how to use snmptrapd with SNMPv3 protected notifications you need to understand some basic concepts. Specifically, please read:

  • SNMPv3 Options -- Documents how to use Net-SNMP with SNMPv3 in general
  • TUT:snmptrap -- Discussing SNMP notifications and sending them using snmptrap
  • TUT:snmptrap SNMPv3 -- Discussing SNMPv3 notifications and sending them using snmptrap

SNMP INFORMs vs SNMP TRAPs Notifications

SNMP supports two types of notifications: TRAPs and INFORMs. (In SNMPv1, there was only TRAPs; SNMPv2c and SNMPv3 support INFORMs too). There is one fundamental difference between SNMP INFORMs and TRAPs:

TRAPs
Sent by an application or daemon but no response is sent or expected by the notification receiver.
INFORMs
INFORMs are nothing more than an acknowledged TRAP. I.E., when the notification receiver receives an INFORM it sends a response back that indicates "I got it". (An application may be configured to send more than one INFORM message if it failed to receive an acknowledgment)

SNMPv3 INFORMs vs SNMP TRAPs

SNMPv3 with the User-Based Security Model (USM) makes use of an EngineID identifier for the SNMPv3 application that is authoratative (meaning the one who controls the flow of information).

With SNMPv3 TRAPs, the authoratative engine is the engine that sends the trap

With SNMPv3 INFORMs, the authoratative engine is the engine that receives the trap.

SNMPv3 USM users are uniquely defined by a combination of the authoratative EngineID and the user name.

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