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SNMP, understanding, MIB-files, MIB-browser

MIB-files

Whom to ask for SNMP-values

You can check out a lot of values by SNMP. You have to install an snmp-daemon on your pc which supplies you with snmp-data. This is possible in Linux, Windows and Vmware ESX too!
I a lot of devices there is already an snmpd installed, for example in network-switches. These devices are called managable and usually cost more money than simpler devices.

What are MIB-files

Dealing with SNMP is dealing with long numbers looking like this: .1.3.6.1.4.1.232.6.2.9.3.1.4.0.1

Nobody know what this long number means. You can compare it with a directory structure which is not made by names but by numbers. There are textfiles which declare what these numbers mean. See this example from the file cpqhlth.mib (this means Compaq Health MIB)

-- The compaq enterprise               (1.3.6.1.4.1.232)
--      cpqHealth Group                (1.3.6.1.4.1.232.6)
--       cpqHeComponent Group          (1.3.6.1.4.1.232.6.2)
--        cpqHeFltTolPowerSupply Group (1.3.6.1.4.1.232.6.2.9)
--         cpqHeFltTolPowerSupplyTable (1.3.6.1.4.1.232.6.2.9.3)
[...]
    CpqHeFltTolPowerSupplyEntry ::= SEQUENCE {
        cpqHeFltTolPowerSupplyChassis             INTEGER,
        cpqHeFltTolPowerSupplyBay                 INTEGER,
        cpqHeFltTolPowerSupplyPresent             INTEGER,
        cpqHeFltTolPowerSupplyCondition           INTEGER,
        cpqHeFltTolPowerSupplyStatus              INTEGER,
        cpqHeFltTolPowerSupplyMainVoltage         INTEGER,
        cpqHeFltTolPowerSupplyCapacityUsed        INTEGER,
        cpqHeFltTolPowerSupplyCapacityMaximum     INTEGER,
        cpqHeFltTolPowerSupplyRedundant           INTEGER,
        cpqHeFltTolPowerSupplyModel               DisplayString,
        cpqHeFltTolPowerSupplySerialNumber        DisplayString,
        cpqHeFltTolPowerSupplyAutoRev             OCTET STRING,
        cpqHeFltTolPowerSupplyHotPlug             INTEGER,
        cpqHeFltTolPowerSupplyFirmwareRev         DisplayString,
        cpqHeFltTolPowerSupplyHwLocation          DisplayString,
        cpqHeFltTolPowerSupplySparePartNum        DisplayString,
        cpqHeFltTolPowerSupplyRedundantPartner    INTEGER
    }
[...]
    cpqHeFltTolPowerSupplyCondition OBJECT-TYPE
        SYNTAX  INTEGER {
            other(1),
            ok(2),
            degraded(3),
            failed(4)
            }
        ACCESS  read-only
        STATUS  mandatory
        DESCRIPTION
            "The condition of the power supply.

            This value will be one of the following:

            other(1)
              The status could not be determined or not present.

            ok(2)
              The power supply is operating normally.

            degraded(3)
              A temperature sensor, fan or other power supply component is
              outside of normal operating range.

            failed(4)
              A power supply component detects a condition that could
              permanently damage the system."
        ::= { cpqHeFltTolPowerSupplyEntry 4 }

You don't have to understand this completely. In this example browse with your MIB-browser the oid mentioned in the first lines .1.3.6.1.4.1.232.6.2.9.3 and try to interpret the values you get together with the MIB-file.

Where to get MIB-files

MIB-files help you to understand which questions you can ask to your device. There are common MIB-files where there are values nearly every device can interpret. But there are also special MIB-files for special devices (Network attached storage, network filer, temperature devices etc.). I will give you some hints where to find these files:

How to browse an SNMP-tree?

You have to have managable device. For example a network-switch. The device itself has an ip-address and a community name (which is simply a password to get values from the device, the default value is "public").

Just take a MIB-Browser (see below), navigate to your device-ip (don't take dns-names, I don't know why they don't work so often with this programs) and get subtree of: .1.3.6.1.2.1.1 which gives you a system-description.

Tools to browse SNMP-values from your device

There is a lot of bad software in the internet. Most good tools must be bought and costs more than 200 $. See my suggestions:

Impressum