Search code examples
snmpnullablemib

How can I properly respond with a null value to an SNMP (2c) GetRequest?

I am developing an SNMP (2c) agent for a sensor product. I'm just learning about SNMP and MIB formats and struggling to represent a particular value that could be unknown.

For example, I've defined a temperature OBJECT-TYPE as an Integer32 but sometimes the value is not available or unknown. If I respond with a null value, the SNMP manager times out*. I would prefer to use a null value when the temperature value is unknown or not available, instead of agreeing upon some specific value to mean the same thing.

This leads me to the following questions:

  1. Does SNMP v2c/MIB support a data type that is analogous to a nullable integer?
  2. If so, what is the proper way to denote this in the MIB?

* I am using MG-SOFT's MIB Browser to get values as a testing method. If the value is null, it times out (even though the agent responded). If the value is an integer, it works as expected. I am using nSoftware IP*Works! SNMP library to develop the agent.

Solution

  • Posting from comment:

    You should not be doing this. OID values should always be singular they should not be dynamically changed, if someone will use a mibfile for this it will be incorrect and misleading for the person who is implementing communication protocol for this sensor. The correct way to do it is to have 2 OIDs one with the value and another with the status of the sensor.