An SNMP trap is a notification event sent by a managed device over a network when a change-of-state (COS) event
occurs. Some events that will cause a device to send SNMP traps include power outages, security breaches, and other
major events. However, devices will also send traps for simple status events, such as doors opening and closing.
These traps are sent across the network in the same manner, and are given no priority when using a standard SNMP
Trap Messages From SNMP Devices Managed by One SNMP Application
Simple Network Management Protocol (SNMP) is used when sending trap communications across a network to the device
manager. In some cases, SNMP alleviates managers of the responsibility of requesting information from every device
along a network individually. Instead, managed devices send unsolicited notification in the form of autonomous traps
to one common SNMP network monitoring application.
Managers then receive the SNMP trap, and can take action based upon the event described by the trap. Managers
cannot send a trap message back to a device, however, as trap communication only occurs from device to network
manager. The management application must notify the proper person of the event.
Autonomous Traps Notify You of All Critical Alarm Events
SNMP trap requests can fall under two categories, polled or autonomous. When an SNMP manager
operates using polled
SNMP traps, it will periodically request updates from all managed devices. This is done according a specific time
frame, such as every half hour, or every five minutes. When traps are autonomous, they are automatically sent to the
manager any time a COS event occurs. Rather than updating the manager on the status of a door every few minutes,
autonomous SNMP traps are sent every time a door opens or closes.
An SNMP Alarm can be Identified Through Trap ID Granularity or Through Variable Bindings
traps sent from devices generally conform to 1 of 2 major trap systems: granular or variable bindings. When a
trap message is assembled in the granular format, each individual trap is given a trap identifier rather than a
Variable Binding Style (VBS). This identifier is a number that is recognized by the SNMP manager to indicate a
particular state change, such as a specific door opening. T/Mon
makes use of this message format.
Other SNMP managers assemble their traps in the VBS format, which assign each trap the same trap ID number and
store alarm data in the variable bindings of the trap. The messages differentiate by giving a different detail
message for each trap, such as indicating a door is open, or a battery charge is low.
Learn More About SNMP Traps and How They Work for Your Network
SNMP Trap Basics
Using SNMP Traps in a Network Management System
In-Depth Look at SNMP MIBs
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