# Agent-side MIB implementations

## Implementing scalar MIB objects

Listen and respond to SNMP GET/SET/GETNEXT/GETBULK queries with the following options:

- SNMPv2c

- with SNMP community “public”

- serving custom Managed Object Instance defined within this script

- allow read access only to the subtree where the custom MIB object resides

- over IPv4/UDP, listening at 127.0.0.1:161

The following Net-SNMP commands will walk this Agent:

$ snmpwalk -v2c -c public 127.0.0.1 .1.3.6

    import sys
    from pysnmp.entity import engine, config
    from pysnmp.entity.rfc3413 import cmdrsp, context
    from pysnmp.carrier.asyncore.dgram import udp
    from pysnmp.proto.api import v2c

    # Create SNMP engine
    snmpEngine = engine.SnmpEngine()

    # Transport setup

    # UDP over IPv4
    config.addTransport(
        snmpEngine,
        udp.domainName,
        udp.UdpTransport().openServerMode(('127.0.0.1', 161))
    )

    # SNMPv2c setup

    # SecurityName <-> CommunityName mapping.
    config.addV1System(snmpEngine, 'my-area', 'public')

    # Allow read MIB access for this user / securityModels at VACM
    config.addVacmUser(snmpEngine, 2, 'my-area', 'noAuthNoPriv', (1, 3, 6, 5))

    # Create an SNMP context
    snmpContext = context.SnmpContext(snmpEngine)

    # --- create custom Managed Object Instance ---

    mibBuilder = snmpContext.getMibInstrum().getMibBuilder()

    MibScalar, MibScalarInstance = mibBuilder.importSymbols(
        'SNMPv2-SMI', 'MibScalar', 'MibScalarInstance'
    )

    class MyStaticMibScalarInstance(MibScalarInstance):
        # noinspection PyUnusedLocal,PyUnusedLocal
        def getValue(self, name, idx):
            return self.getSyntax().clone(
                'Python %s running on a %s platform' % (sys.version, sys.platform)
            )

    mibBuilder.exportSymbols(
        '__MY_MIB', MibScalar((1, 3, 6, 5, 1), v2c.OctetString()),
        MyStaticMibScalarInstance((1, 3, 6, 5, 1), (0,), v2c.OctetString())
    )

    # --- end of Managed Object Instance initialization ----

    # Register SNMP Applications at the SNMP engine for particular SNMP context
    cmdrsp.GetCommandResponder(snmpEngine, snmpContext)
    cmdrsp.NextCommandResponder(snmpEngine, snmpContext)
    cmdrsp.BulkCommandResponder(snmpEngine, snmpContext)

    # Register an imaginary never-ending job to keep I/O dispatcher running forever
    snmpEngine.transportDispatcher.jobStarted(1)

    # Run I/O dispatcher which would receive queries and send responses
    try:
        snmpEngine.transportDispatcher.runDispatcher()
    except:
        snmpEngine.transportDispatcher.closeDispatcher()
        raise

`Download` script.

## Implementing conceptual table

Listen and respond to SNMP GET/SET/GETNEXT/GETBULK queries with the following options:

- SNMPv2c

- with SNMP community “public”

- define a simple SNMP Table within a newly created EXAMPLE-MIB

- pre-populate SNMP Table with a single row of values

- allow read access only to the subtree where example SNMP Table resides

- over IPv4/UDP, listening at 127.0.0.1:161

The following Net-SNMP commands will populate and walk a table:

$ snmpset -v2c -c public 127.0.0.1 1.3.6.6.1.5.2.97.98.99 s “my value”
$ snmpset -v2c -c public 127.0.0.1 1.3.6.6.1.5.4.97.98.99 i 4
$ snmpwalk -v2c -c public 127.0.0.1 1.3.6

…while the following command will destroy the same row

$ snmpset -v2c -c public 127.0.0.1 1.3.6.6.1.5.4.97.98.99 i 6
$ snmpwalk -v2c -c public 127.0.0.1 1.3.6

    from pysnmp.entity import engine, config
    from pysnmp.entity.rfc3413 import cmdrsp, context
    from pysnmp.carrier.asyncore.dgram import udp
    from pysnmp.proto.api import v2c

    # Create SNMP engine
    snmpEngine = engine.SnmpEngine()

    # Transport setup

    # UDP over IPv4
    config.addTransport(
        snmpEngine,
        udp.domainName,
        udp.UdpTransport().openServerMode(('127.0.0.1', 161))
    )

    # SNMPv2c setup

    # SecurityName <-> CommunityName mapping.
    config.addV1System(snmpEngine, 'my-area', 'public')

    # Allow read MIB access for this user / securityModels at VACM
    config.addVacmUser(snmpEngine, 2, 'my-area', 'noAuthNoPriv', (1, 3, 6, 6), (1, 3, 6, 6))

    # Create an SNMP context
    snmpContext = context.SnmpContext(snmpEngine)

    # --- define custom SNMP Table within a newly defined EXAMPLE-MIB ---

    mibBuilder = snmpContext.getMibInstrum().getMibBuilder()

    (MibTable,
     MibTableRow,
     MibTableColumn,
     MibScalarInstance) = mibBuilder.importSymbols(
        'SNMPv2-SMI',
        'MibTable',
        'MibTableRow',
        'MibTableColumn',
        'MibScalarInstance'
    )

    RowStatus, = mibBuilder.importSymbols('SNMPv2-TC', 'RowStatus')

    mibBuilder.exportSymbols(
        '__EXAMPLE-MIB',
        # table object
        exampleTable=MibTable((1, 3, 6, 6, 1)).setMaxAccess('readcreate'),
        # table row object, also carries references to table indices
        exampleTableEntry=MibTableRow((1, 3, 6, 6, 1, 5)).setMaxAccess('readcreate').setIndexNames((0, '__EXAMPLE-MIB', 'exampleTableColumn1')),
        # table column: string index
        exampleTableColumn1=MibTableColumn((1, 3, 6, 6, 1, 5, 1), v2c.OctetString()).setMaxAccess('readcreate'),
        # table column: string value
        exampleTableColumn2=MibTableColumn((1, 3, 6, 6, 1, 5, 2), v2c.OctetString()).setMaxAccess('readcreate'),
        # table column: integer value with default
        exampleTableColumn3=MibTableColumn((1, 3, 6, 6, 1, 5, 3), v2c.Integer32(123)).setMaxAccess('readcreate'),
        # table column: row status
        exampleTableStatus=MibTableColumn((1, 3, 6, 6, 1, 5, 4), RowStatus('notExists')).setMaxAccess('readcreate')
    )

    # --- end of custom SNMP table definition, empty table now exists ---

    # --- populate custom SNMP table with one row ---

    (exampleTableEntry,
     exampleTableColumn2,
     exampleTableColumn3,
     exampleTableStatus) = mibBuilder.importSymbols(
        '__EXAMPLE-MIB',
        'exampleTableEntry',
        'exampleTableColumn2',
        'exampleTableColumn3',
        'exampleTableStatus'
    )
    rowInstanceId = exampleTableEntry.getInstIdFromIndices('example record one')
    mibInstrumentation = snmpContext.getMibInstrum()
    mibInstrumentation.writeVars(
        ((exampleTableColumn2.name + rowInstanceId, 'my string value'),
         (exampleTableColumn3.name + rowInstanceId, 123456),
         (exampleTableStatus.name + rowInstanceId, 'createAndGo'))
    )

    # --- end of SNMP table population ---

    # Register SNMP Applications at the SNMP engine for particular SNMP context
    cmdrsp.GetCommandResponder(snmpEngine, snmpContext)
    cmdrsp.SetCommandResponder(snmpEngine, snmpContext)
    cmdrsp.NextCommandResponder(snmpEngine, snmpContext)
    cmdrsp.BulkCommandResponder(snmpEngine, snmpContext)

    # Register an imaginary never-ending job to keep I/O dispatcher running forever
    snmpEngine.transportDispatcher.jobStarted(1)

    # Run I/O dispatcher which would receive queries and send responses
    try:
        snmpEngine.transportDispatcher.runDispatcher()
    except:
        snmpEngine.transportDispatcher.closeDispatcher()
        raise

`Download` script.

## Serve non-default MIB tree

Listen and respond to SNMP GET/SET/GETNEXT/GETBULK queries with the following options:

- SNMPv3

- with USM username usr-md5-none

- using alternative set of Managed Objects addressed by contextEngineId: 8000000001020304, contextName: my-context

- allow access to SNMPv2-MIB objects (1.3.6.1.2.1)

- over IPv4/UDP, listening at 127.0.0.1:161

Either of the following Net-SNMP commands will walk this Agent:

$ snmpwalk -v3 -u usr-md5-none -l authNoPriv -A authkey1 -E 8000000001020304 -n my-context 127.0.0.1 .1.3.6
$ snmpwalk -v3 -u usr-md5-none -l authNoPriv -A authkey1 -E 8000000001020304 127.0.0.1 .1.3.6

    from pysnmp.entity import engine, config
    from pysnmp.entity.rfc3413 import cmdrsp, context
    from pysnmp.carrier.asyncore.dgram import udp
    from pysnmp.smi import instrum, builder
    from pysnmp.proto.api import v2c

    # Create SNMP engine
    snmpEngine = engine.SnmpEngine()

    # Transport setup

    # UDP over IPv4
    config.addTransport(
        snmpEngine,
        udp.domainName,
        udp.UdpTransport().openServerMode(('127.0.0.1', 161))
    )

    # SNMPv3/USM setup

    # user: usr-md5-none, auth: MD5, priv NONE
    config.addV3User(
        snmpEngine, 'usr-md5-none',
        config.usmHMACMD5AuthProtocol, 'authkey1'
    )

    # Allow full MIB access for each user at VACM
    config.addVacmUser(snmpEngine, 3, 'usr-md5-none', 'authNoPriv', (1, 3, 6, 1, 2, 1), (1, 3, 6, 1, 2, 1))

    # Create an SNMP context with ContextEngineId = 8000000001020304
    snmpContext = context.SnmpContext(
        snmpEngine, contextEngineId=v2c.OctetString(hexValue='8000000001020304')
    )

    # Create an [empty] set of Managed Objects (MibBuilder), pass it to
    # Management Instrumentation Controller and register at SNMP Context
    # under ContextName 'my-context'
    snmpContext.registerContextName(
        v2c.OctetString('my-context'),  # Context Name
        instrum.MibInstrumController(builder.MibBuilder())  # Managed Objects
    )

    # Register SNMP Applications at the SNMP engine for particular SNMP context
    cmdrsp.GetCommandResponder(snmpEngine, snmpContext)
    cmdrsp.SetCommandResponder(snmpEngine, snmpContext)
    cmdrsp.NextCommandResponder(snmpEngine, snmpContext)
    cmdrsp.BulkCommandResponder(snmpEngine, snmpContext)

    # Register an imaginary never-ending job to keep I/O dispatcher running forever
    snmpEngine.transportDispatcher.jobStarted(1)

    # Run I/O dispatcher which would receive queries and send responses
    try:
        snmpEngine.transportDispatcher.runDispatcher()
    except:
        snmpEngine.transportDispatcher.closeDispatcher()
        raise

`Download` script.

## Custom MIB Controller

Listen and respond to SNMP GET/SET/GETNEXT/GETBULK queries with the following options:

- SNMPv3

- with USM username usr-none-none

- using alternative set of Managed Objects addressed by contextName: my-context

- allow access to SNMPv2-MIB objects (1.3.6.1.2.1)

- over IPv4/UDP, listening at 127.0.0.1:161

The following Net-SNMP command will send GET request to this Agent:

$ snmpget -v3 -u usr-none-none -l noAuthNoPriv -n my-context -Ir 127.0.0.1 sysDescr.0

    from pysnmp.entity import engine, config
    from pysnmp.entity.rfc3413 import cmdrsp, context
    from pysnmp.carrier.asyncore.dgram import udp
    from pysnmp.smi import instrum
    from pysnmp.proto.api import v2c

    # Create SNMP engine
    snmpEngine = engine.SnmpEngine()

    # Transport setup

    # UDP over IPv4
    config.addTransport(
        snmpEngine,
        udp.domainName,
        udp.UdpTransport().openServerMode(('127.0.0.1', 161))
    )

    # SNMPv3/USM setup

    # user: usr-none-none, auth: NONE, priv NONE
    config.addV3User(
        snmpEngine, 'usr-none-none'
    )

    # Allow full MIB access for each user at VACM
    config.addVacmUser(snmpEngine, 3, 'usr-none-none', 'noAuthNoPriv', (1, 3, 6, 1, 2, 1), (1, 3, 6, 1, 2, 1))

    # Create an SNMP context
    snmpContext = context.SnmpContext(snmpEngine)

    # Very basic Management Instrumentation Controller without
    # any Managed Objects attached. It supports only GET's and
    # always echos request var-binds in response.
    class EchoMibInstrumController(instrum.AbstractMibInstrumController):
        def readVars(self, varBinds, acInfo=(None, None)):
            return [(ov[0], v2c.OctetString('You queried OID %s' % ov[0])) for ov in varBinds]

    # Create a custom Management Instrumentation Controller and register at
    # SNMP Context under ContextName 'my-context'
    snmpContext.registerContextName(
        v2c.OctetString('my-context'),  # Context Name
        EchoMibInstrumController()  # Management Instrumentation
    )

    # Register GET&SET Applications at the SNMP engine for a custom SNMP context
    cmdrsp.GetCommandResponder(snmpEngine, snmpContext)
    cmdrsp.SetCommandResponder(snmpEngine, snmpContext)

    # Register an imaginary never-ending job to keep I/O dispatcher running forever
    snmpEngine.transportDispatcher.jobStarted(1)

    # Run I/O dispatcher which would receive queries and send responses
    try:
        snmpEngine.transportDispatcher.runDispatcher()
    except:
        snmpEngine.transportDispatcher.closeDispatcher()
        raise

`Download` script.

See also: library reference.