When SNMP is not working — a troubleshooting guide

Simple Network Management Protocol (SNMP) is the de facto standard for monitoring network-connected devices such as printers, switches, servers, and firewalls. When many devices are connected, troubleshooting the SNMP is notoriously awkward. Here’s what you should look for when SNMP is not working.

Having a new networked copier/printer installed in the office but not being able to monitor it often creates lots of pain. When the SNMP is not working, you cannot see simple things like a printer running out of ink. This is frustrating as the missing supplies are always urgent and the VP of Sales needs that monthly sales report printed right now.

Useful tools when SNMP is not working

So what’s the best practice for troubleshooting? If your networked SNMP devices are NOT responding correctly to your queries, it can be a cumbersome job to find the ones that are NOT working. But it doesn’t have to be like this!

There are several free applications available for executing an SNMP query—some with a GUI and others that use fairly simple command lines.

We recommend the simple but highly effective command-line tool SnmpWalk.

SNMP Troubleshooting in the command line using SNMPwalkIf you’re a Microsoft Windows user, consider downloading this ready-to-use package. Otherwise install a version matching your type of OS. Packages exist for Mac OS X and different flavors of Linux/Unix as well.

Is it turned on at all?

Most devices have SNMP enabled by default. However, some devices need this done manually. Switches from Cisco and Dell are known for this. If you do not enable the SNMP, you’ll never get any feedback.

When you have your SNMP tool installed and ready to use, your next step in investigating why SNMP is not working is to decipher the result produced by the tool.

Say, you get a valid reply from an SNMP-enabled device. Now you need to figure out which values are of interest. Depending on the documentation available, this may prove a most tedious task.

Understanding OID values

OID Descriptions are useful when SNMP is not workingThe SNMP stores values in a tree-like structure similar to how files and folders are organized on your hard drive. Each vendor may implement a private branch with specific information about the hardware or use a more generic structure defined by, for example, RFC 1156.
If you want to better understand such results, you can use one of the free tools available, where you simply enter the OID value (ISO Number).

Tools that can help you understand what you’re looking at include

The next step in SNMP troubleshooting

If you want to read more about SNMP troubleshooting, try our simple step-by-step guide: How to test if SNMP devices are responding correctly to SNMP queries.

This short guide will NOT make you a PhD in SNMP queries, but it will adequately prepare you for most occasions and provide the tools needed for most troubleshooting.

Use this guide and you’ll soon master the tools needed, get a better understanding of how the SNMP works, and, most importantly, ensure that devices correctly replay to your queries.

Ready to explore more SNMP devices in your network?

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