MIB Creation guide

First, say that this is basically a quick 'n' dirty guide to create a MIB file needed if you want to implement some specific SNMP monitoring on your own. Don't take it too seriously or trustable/standard way to implement things.

Comments start with '–' (two dashes) until EOL.

First line should define the MIB name (i.e. TEST-MIB), and indicate the start its definition. The entire defintion (and hence the file) should end with END ;)

TEST-MIB DEFINITIONS ::= BEGIN
(...)
END

Immeditaley after that, we should indicate which SNMP modules (either other MIBS, types definitions formats, … we need to use and on which MIBs they are found. This is done with IMPORTS, and we specify the type of element to import, elements to import and from which MIB, like:

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE,Counter32, Gauge32, enterprises       FROM SNMPv2-SMI
    TEXTUAL-CONVENTION, DisplayString,                                 FROM SNMPv2-TC
    MODULE-COMPLIANCE, OBJECT-GROUP,                                   FROM SNMPv2-CONF

You will always need to import something, as your MIB will 'hang' (inherit) from another MIB tree you should import at least that MIB to indicat you are hangingover that tree. Usually enterprises

Start naming and defining our stuff, the name of the module with some other informative data;

  testMIB MODULE-IDENTITY
      LAST-UPDATED "200304121008Z"
      ORGANIZATION "Lady 3Jane"
      CONTACT-INFO "Marc Franquesa
                    Lady 3Jane
                    Vic"
      DESCRIPTION  "Descripció de vàries línies
                    del MIB"
      REVISION     "200304121008Z"
      ::= { enterprises 5505 }

Some important details on that:

• The last line ::= is important: it defines from which point of the tree the MIB will hang, in this case below enterprises with number 5505, so the OID of the root of our MIB will be .1.3.6.1.4.1.5505
• Dates are UTC format and seems is checked that LAST-UPDATED matches REVISION

Frist there are branch nodes, which serve only to structure the tree hierarchy in different branches inside our tree. They don't contian any information, are simply 'structural' nodes:

testMIBObjects    OBJECT IDENTIFIER ::= { testMIB 1 }
testConformance   OBJECT IDENTIFIER ::= { testMIB 2 }
testGroups        OBJECT IDENTIFIER ::= { testConformance 1 }

Let's start defining something really useful, and object which can hold data.

testItem  OBJECT-TYPE
    SYNTAX      Counter32
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION "Descripció del valor"
    ::= { testMIB 1 }

Notes:

The last part ::= { name #num } indicates from which object will hang the element and on which index.

First the table itself should be defined:

ifTable OBJECT-TYPE
    SYNTAX      SEQUENCE OF IfEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
            "A list of interface entries.  The number of entries is
            given by the value of ifNumber."
    ::= { interfaces 2 }

Like an object, but note the SYNTAX is now a SEQUENCE of something, let's go to define that:

The 'Entry' need to be defined to indicate which filed will be used as an Index:

ifEntry OBJECT-TYPE
    SYNTAX      IfEntry
    MAX-ACCESS  not-accessible
    STATUS      current
    DESCRIPTION
            "An entry containing management information applicable to a
            particular interface."
    INDEX   { ifIndex }
    ::= { ifTable 1 }

Also like an object, but this time note the INDEX part which indicate which part of the object will bu used to index it inside the table.

The Index needs to be defined as well:

ifIndex OBJECT-TYPE
    SYNTAX      InterfaceIndex
    MAX-ACCESS  read-only
    STATUS      current
    DESCRIPTION
            "A unique value, greater than zero, for each interface.  It
            is recommended that values are assigned contiguously
            starting from 1.  The value for each interface sub-layer
            must remain constant at least from one re-initialization of
            the entity's network management system to the next re-
            initialization."
    ::= { ifEntry 1 }

Finally we define the elements inside an Entry:

IfEntry ::=
    SEQUENCE {
        ifIndex                 InterfaceIndex,
        ifDescr                 DisplayString,
        ifType                  IANAifType,
        ifMtu                   Integer32,
        ifSpeed                 Gauge32,
        ifPhysAddress           PhysAddress,
        ifAdminStatus           INTEGER,
        ifOperStatus            INTEGER,
        ifLastChange            TimeTicks,
        ifInOctets              Counter32
  }

Note that you should define now each filed separatedly too.