Home / server / Questions / 974141
Accepted
confoundr
Asked: 2019-07-06 11:09:35 +0800 CST

How to Determine the Correct OID to Use for Monitoring

  • 772

Is there a correct/better way of determining the correct OID to use for SNMP monitoring?

I was able to download the MIB directly from the device, but I am lost on finding the correct OID from the list of hundreds of OIDs. All forums that I've come across have a different model OID, or simply say "use the OID and you'll be good" without details...

Steps Taken

  • downloaded the MIB from the device
  • Verified I could ping the device
  • Verified I could run snmpwalk on the device (NOTE I am not familiar with all features and usage of snmpwalk)
snmp

2 Answers

  1. Best Answer

    From my experience, sadly no, I had to get the MIB and try to find in them the correct thing I need to query. (I used a simple mib browser)

    For the OID you found, temperature too high, be sure it’s not a boolean value that set it at on/1 when it trigger, it could explain why you read nothing if the device is operating under normal temperature.

    Sadly OID usage and documentation is underated online and not popular. I used to create monitoring templates inside a monitoring tool for unknown device from the tool, and I was seen as a black magic user to do so..

    The only tip I can tell is watch for the return value, some are string even if they are wrote as a number, and other are simply integer.

    • 2

  2. While a MIB browser can indeed help, you can do a lot of parsing with the NET-SNMP snmptranslate command. There are quite a few options, so consult its man page, but here are a couple of examples.

    Let's say I have downloaded MIBs for a Synology device and want to monitor it. I can use snmptranslate to take a peek in the MIBs in a more user-friendly way than just reading the raw MIB file.

    To start, I will check out SYNOLOGY-SYSTEM-MIB.txt I have downloaded.

    • Let's find out the actual name of the MIB. Sometimes it is the same as the name of the MIB file, but not always. Statement DEFINITIONS is used to define the name of the MIB.

       $ grep DEFINITIONS SYNOLOGY-SYSTEM-MIB.txt
 SYNOLOGY-SYSTEM-MIB DEFINITIONS ::= BEGIN

      So now I know that the MIB is called SYNOLOGY-SYSTEM-MIB.

    • Next, I will look inside to find the top OID defined in it:

      $ grep MODULE-IDENTITY SYNOLOGY-SYSTEM-MIB.txt
enterprises, MODULE-IDENTITY, OBJECT-TYPE, Integer32
synoSystem MODULE-IDENTITY

      The last line is the intersting one, specifically synoSystem. This is the top OID which I can now use to get the structure of the MIB.

    • When polling an OID in text form, MIB::OID notation should be used. This is so snmp command knows which MIB to use to translate the OID into numerical form which agents understand (very similar to the principle of DNS translation):

      $ snmptranslate -Tp SYNOLOGY-SYSTEM-MIB::synoSystem

      And the output is:

      +--synoSystem(1)
   +-- -R-- Integer32 systemStatus(1)
   |        Range: 1..2
   +-- -R-- Integer32 temperature(2)
   +-- -R-- Integer32 powerStatus(3)
   |        Range: 1..2
   |
   +--fan(4)
   |  |
   |  +-- -R-- Integer32 systemFanStatus(1)
   |  |        Range: 1..2
   |  +-- -R-- Integer32 cpuFanStatus(2)
   |           Range: 1..2
   |
   +--dsmInfo(5)
   |  |
   |  +-- -R-- String    modelName(1)
   |  +-- -R-- String    serialNumber(2)
   |  +-- -R-- String    version(3)
   |  +-- -R-- Integer32 upgradeAvailable(4)
   |           Range: 1..5
   |
   +--systemConformance(6)
      |
      +--systemCompliances(1)
      |  |
      |  +--systemCompliance(1)
      |
      +--systemGroups(2)
         |
         +--systemGroup(1)

    • Now, let's say that I am interested in OID upgradeAvailable so that I can tell when I can upgrade the DSM on this box. I can find more details about it by running:

        $ snmptranslate -Td SYNOLOGY-SYSTEM-MIB::upgradeAvailable

      And the output is:

        SYNOLOGY-SYSTEM-MIB::upgradeAvailable
  upgradeAvailable OBJECT-TYPE
    -- FROM       SYNOLOGY-SYSTEM-MIB
    SYNTAX        Integer32 (1..5)
    MAX-ACCESS    read-only
    STATUS        current
    DESCRIPTION   "This oid is for checking whether there is a latest DSM can be upgraded.
           Available(1): There is version ready for download.
           Unavailable(2): The DSM is latest version.
           Connecting(3): Checking for the latest DSM.
           Disconnected(4): Failed to connect to server.
           Others(5): If DSM is upgrading or downloading, the status will show others."
  ::= { iso(1) org(3) dod(6) internet(1) private(4) enterprises(1) synology(6574) synoSystem(1) dsmInfo(5) 4 }

      So now when I actually poll the device, I know I am running the latest DSM:

        $ snmpwalk <snmp parameters> <device> SYNOLOGY-SYSTEM-MIB::upgradeAvailable
  SYNOLOGY-SYSTEM-MIB::upgradeAvailable.0 = INTEGER: 2

    Hope this helps someone.

    • 1