SNMP Trap FAQ: Basics for Telecom Network Monitoring

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If you're a professional who manages a significant telecom/corporate network, you'll likely need to use the SNMP protocol. This basic FAQ list will get your started. If your interest is merely to learn about SNMP in a general sense, please remember that the answers below were written with enterprise-grade systems in mind.

What is an SNMP trap?

An SNMP trap is a warning event sent by a managed device over a network when a change-of-state (COS) event occurs. Some events that will trigger a device to send SNMP traps include power outages and security breaches. 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 manager.

SNMP trap requests can fall under two groups, polled or autonomous. When an SNMP manager operates using polled SNMP traps, it will periodically request updates from all managed devices. This is accomplished according to a single 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.

How can an SNMP trap alarm be identified?

SNMP traps sent from devices usually conform to 1 of 2 major trap systems: granular or variable bindings. When a trap message is assembled in the granular format, each single trap is specified a trap identifier rather than a Variable Binding Style (VBS). This identifier is a number that is accepted by the SNMP manager to indicate a particular state change, such as a single door opening. The messages are set apart by providing a different detail message for each trap, such as indicating a door is open, or a battery charge is low.

What are some SNMP Trap issues?

It is often the case that SNMP problems are caused by the content of SNMP traps being sent. Therefore, it is important to check for these SNMP trap issues.

Why would I need to use an SNMP trap device in my network?

SNMP is primarily used when sending trap communications through a network to the device manager. In some situations, SNMP relieves you of the job of requesting information from every device along a network individually. Instead, managed devices send unsolicited alert in the form of autonomous traps to one common SNMP network monitoring application.

Once you receive the SNMP trap, you can take action based upon the event described by the SNMP trap. However, you cannot send an SNMP trap message back to a device, as SNMP trap communication only occurs from device to network manager. The management application must inform the appropriate person of the event.

How would I select an SNMP trap management system?

Look for these key features:

Why is a typical SNMP manager not sufficient for monitoring my network?

Solely relying on an SNMP manager for your key network monitoring does not take into account the vast amount of legacy and non-SNMP equipment that is working perfectly fine in networks around the world. The role of an SNMP manager is best used for performing an inventory of network devices and drilling down into gear details after your network monitoring system notifies you of an issue. SNMP is only one item in your network alarm monitoring toolkit, and it can be used more effectively when it is part of your total network monitoring solution.

What are some common mistakes typically made when integrating SNMP and non-SNMP monitoring? How does the communication work?

The SNMP manager sends a Get or GetNext message to read a variable and the agent's response contains the requested information if managed. The manager then sends a Set to change a variable and the agent's response confirms the change if allowed. The agent sends a Trap when a specific event occurs.

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