How to monitor ESXi host hardware with SNMP

The Simple Network Management Protocol (SNMP) is a protocol for monitoring and configuration of network-attached devices. SNMP exposes data in the form of variables and values. These variables can then be queried or set. A query retrieves the value of a variable, a set operation assigns a value to a variable. The variables are organized in a hierarchy and each variable is identified by an object identifiers (OID). The management information base (MIB ) describes this hierarchy. MIB files (simple text files) contain metadata for each OID. These are necessary for the translation of a numeric OID into a human-readable format.  SNMP knows two devices types:

  • the managed device which runs the SNMP agent
  • the network management station (NMS) which runs the management software

The NMS queries the SNMP agent with GET requests. Configuration changes are made using SET requests. The SNMP agent can inform the NMS about state changes using a SNMP trap message. The easiest way for authentication is the SNMP community string.

SNMP is pretty handy and it’s still used, especially for monitoring and managing networking components. SNMP has the benefit, that it’s very lightweight. Monitoring a system with WBEM or using an API can cause slightly more load, compared to SNMP. Furthermore, SNMP is a internet-protocol standard. Nearly every device supports SNMP.

Monitoring host hardware with SNMP

Why should I monitor my ESXi host hardware with SNMP? The vCenter Server can trigger an alarm and most customers use applications like VMware vRealize Operations, Microsoft System Center Operations Manager, or HPE Systems Insight Manager (SIM). There are better ways to monitor the overall health of an ESXi host. But sometimes you want to get some stats about the network interfaces (throughput), or you have a script that should do something, if a NIC goes down or something else happens. Again, SNMP is very resource-friendly and widely supported.

Configure SNMP on ESXi

I focus on ESXi 5.1 and beyond. The ESXi host is called “the SNMP Agent”. We don’t configure traps or trap destinations. We just want to poll the SNMP agent using SNMP GET requests. The configuration is done using esxcli . First of all, we need to set a community string and enable SNMP.

That’s it! The necessary firewall ports and services are opened and started automatically.

Querying the SNMP agent

I use a CentOS VM to show you some queries. The Net-SNMP package contains the tools snmpwalk  and  snmpget. To install the Net-SNMP utils, simply use yum .

Download the VMware SNMP MIB files, extract the ZIP file, and copy the content to to /usr/share/snmp/mibs.

Now we can use snmpwalk  to “walk down the hierarchy “. This is only a small part of the complete output. The complete snmpwalk  output has more than 4000 lines!

Now we can search for interesting parts. If you want to monitor the link status of the NICs, try this:

As you can see, I used a subtree of the whole hierarchy (IF-MIB::ifDescr). This is the “translated” OID. To get the numeric OID, you have to add the option  -O fn to snmpwalk .

You can use snmptranslate  to translate an OID.

So far, we have only the description of the interfaces. With a little searching, we find the status of the interfaces (I stripped the output).

ifOperStatus.1  corresponds with ifDescr.1 , ifOperStatus.2  corresponds with ifDescr.2  and so on. The ifOperStatus corresponds  with the status of the NICs in the vSphere Web Client.

nic_status_web_client

If you want to monitor the fans or power supplies, use these these OIDs.

Many possibilities

SNMP offers a simple and lightweight way to monitor a managed device. It’s not a replacement for vCenter, vROps or SCOM. But it can be an addition, especially because SNMP is an internet-protocol standard.

How to monitor ESXi host hardware with SNMP
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Patrick Terlisten
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Patrick Terlisten

vcloudnine.de is the personal blog of Patrick Terlisten. Patrick has a strong focus on virtualization & cloud solutions, but also storage, networking, and IT infrastructure in general. He is a fan of Lean Management and agile methods, and practices continuous improvement whereever it is possible.

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Patrick Terlisten
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