Simple Network Management Protocol (SNMP)

What is Simple Network Management Protocol?

SNMP is a protocol which has crossed over from information technology (IT) to PROFINET networks. Most PROFINET devices support it for network diagnostics and measurement through PROFINET’s coexistence with standard IT protocols and industrial Ethernet. Information can be gathered from the network nodes such as statistics of the network load (bandwidth utilization), errors from faulty packets, or status of the switch ports.  This information is critical to determine the health and stability of your industrial networks.  You can access this information by installing a diagnostic software with SNMP support on PC stations. The software will poll the device(s) for information from Management Information Bases (MIBs).  MIBs are network and protocol related data sets (databases) of variables located in the devices, available for readout.

Why is it called simple?

Figure 1 – Reading SNMP Statistics with an HMI

The main reason it is called “simple” is that it supports a small set of commands available for polling information from an SNMP capable device.  It also supports optional ‘traps’ which allows devices that support them to send a message based on an event such as a network load threshold or a network error. Users can access the information both over a local area network (LAN) and remotely over a wide area network (WAN) thanks to UDP/IP transport.

What information is mandatory on a PROFINET device which supports SNMP?

RFC 1213 and LLDP MIBs are required.  See the PROFINET profiles document which is part of the specifications for further details.

How do I get SNMP software?

First, check with your product vendors to determine the support for your devices. Also, check with your IT department who already might have an SNMP capable tool available.  If your IT department does not have a good tool, there are many free and commercial tools available.  Start with the industrial providers first, as they strive to make these tools easy to use for control and application engineers and usually support PROFINET diagnostics as well. As one of our colleagues commonly says: “You can pay early or later, but if you pay later due to expensive network downtime it will always cost more”. PROFINET and SNMP tools are probably in your best interest to catch any network issues before they occur.

Can SNMP work with my HMI?

Of course, see figure 1, this is a picture of a PC based HMI using an SNMP-OPC Server.  Some HMIs also might support SNMP natively.  On the HMI we are reading the port status of the switch ports. It also displays the bandwidth utilization on one of the ports.  You can read more about HMIs here.

How can I tell if my PROFINET device or controller supports SNMP?

Check product documentation or ask the vendor what the PROFINET conformance class for the device is.  For more about conformance classes click here.

My device does not support SNMP or I don’t have a tool readily available, what can I do?

In the rare event, your device does not support SNMP or you do not have a tool, do not be alarmed.  PROFINET devices certified to V2.3 (or higher) of the standard also support reading network statistics and topology information through device data records.  By using an acyclic PROFINET read record request, the data can be read out in a different way, for example directly from your PLC application.PROFINET gives you more than one way to get the information you need in your application.

How to learn more about SNMP?

See this protocol in action and learn more, attend a PROFINET class in your area.