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Using pySNMP to write an SNMP agent (for OpenNMS)

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I'm trying to write a python SNMP agent that I can embed within my python application so that the application can be monitored remotely by OpenNMS. OpenNMS expects the Agent to implement the HOST-RESOURCES-MIB querying two fields hrSWRunNameand hrSWRunStatus.

I took a pysnmp example as the basis of my code and edited it as I believed necessary. The resulting code looks like this:

import logging

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


# debug.setLogger(debug.Debug('all'))

formatting = '[%(asctime)s-%(levelname)s]-(%(module)s) %(message)s'
logging.basicConfig(level=logging.DEBUG, format=formatting, )

logging.info("Starting....")

# Create SNMP engine
snmpEngine = engine.SnmpEngine()

# Transport setup

# UDP over IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTransport().openServerMode(('localhost', 12345))
)

# 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, 1, 2, 1),
                   (1, 3, 6, 1, 2, 1))


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

logging.debug('Loading HOST-RESOURCES-MIB module...'),
mibBuilder = builder.MibBuilder().loadModules('HOST-RESOURCES-MIB')
logging.debug('done')

logging.debug('Building MIB tree...'),
mibInstrum = instrum.MibInstrumController(mibBuilder)
logging.debug('done')

logging.debug('Building table entry index from human-friendly representation...')
# see http://www.oidview.com/mibs/0/HOST-RESOURCES-MIB.html
hostRunTable, = mibBuilder.importSymbols('HOST-RESOURCES-MIB', 'hrSWRunEntry')
instanceId = hostRunTable.getInstIdFromIndices(1)
logging.debug('done')


# The following shows the OID name mapping
#
# hrSWRunTable          1.3.6.1.2.1.25.4.2          <TABLE>
# hrSWRunEntry          1.3.6.1.2.1.25.4.2.1        <SEQUENCE>
# hrSWRunIndex          1.3.6.1.2.1.25.4.2.1.1      <Integer32>
# hrSWRunName           1.3.6.1.2.1.25.4.2.1.2      <InternationalDisplayString> 64 Char
# hrSWRunID             1.3.6.1.2.1.25.4.2.1.3      <ProductID>
# hrSWRunPath           1.3.6.1.2.1.25.4.2.1.4      <InternationalDisplayString> 128 octets
# hrSWRunParameters     1.3.6.1.2.1.25.4.2.1.5      <InternationalDisplayString> 128 octets
# hrSWRunType           1.3.6.1.2.1.25.4.2.1.6      <INTEGER>
# hrSWRunStatus         1.3.6.1.2.1.25.4.2.1.7      <INTEGER>  <<===== This is the key variable used by Opennms


# http://docs.opennms.org/opennms/releases/18.0.1/guide-admin/guide-admin.html#_hostresourceswrunmonitor)


logging.debug('Create/update HOST-RESOURCES-MIB::hrSWRunTable table row:')
varBinds = mibInstrum.writeVars((
                                 (hostRunTable.name + (1,) + instanceId, 1),
                                 (hostRunTable.name + (2,) + instanceId, 'AppName'), # <=== Must match OpenNMS service-name variable
                                 (hostRunTable.name + (3,) + instanceId,  {0,0}), #  
                                 (hostRunTable.name + (4,) + instanceId, 'All is well'),
                                 (hostRunTable.name + (5,) + instanceId, 'If this was not the case it would say so here'),
                                 (hostRunTable.name + (6,) + instanceId, 4),# Values are ==> unknown(1), operatingSystem(2), deviceDriver(3), application(4)     
                                 (hostRunTable.name + (7,) + instanceId, 1) #<<=== This is the status number OpenNMS looks at Values are ==> running(1), runnable(2), notRunnable(3), invalid(4)
                                 ))

for oid, val in varBinds:
    print('%s = %s' % ('.'.join([str(x) for x in oid]), val.prettyPrint()))
logging.debug('done')

logging.debug('Read whole MIB (table walk)')
oid, val = (), None
while True:
    oid, val = mibInstrum.readNextVars(((oid, val),))[0]
    if exval.endOfMib.isSameTypeWith(val):
        break
    print('%s = %s' % ('.'.join([str(x) for x in oid]), val.prettyPrint()))
logging.debug('done')

# logging.debug('Unloading MIB modules...'),
# mibBuilder.unloadModules()
# logging.debug('done')


# --- end of  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

The code runs without producing errors. varBinds and MIB Table walk show what I think I should expect:

[2016-12-29 16:42:49,323-INFO]-(SNMPAgent) Starting....
[2016-12-29 16:42:49,470-DEBUG]-(SNMPAgent) Loading HOST-RESOURCES-MIB module...
[2016-12-29 16:42:49,631-DEBUG]-(SNMPAgent) done
[2016-12-29 16:42:49,631-DEBUG]-(SNMPAgent) Building MIB tree...
[2016-12-29 16:42:49,631-DEBUG]-(SNMPAgent) done
[2016-12-29 16:42:49,631-DEBUG]-(SNMPAgent) Building table entry index from human-friendly representation...
[2016-12-29 16:42:49,631-DEBUG]-(SNMPAgent) done
[2016-12-29 16:42:49,632-DEBUG]-(SNMPAgent) Create/update HOST-RESOURCES-MIB::hrSWRunTable table row:
1.3.6.1.2.1.25.4.2.1.1.1 = 1
[2016-12-29 16:42:49,651-DEBUG]-(SNMPAgent) done
1.3.6.1.2.1.25.4.2.1.2.1 = TradeLoader
1.3.6.1.2.1.25.4.2.1.3.1 = 0
1.3.6.1.2.1.25.4.2.1.4.1 = All is well
1.3.6.1.2.1.25.4.2.1.5.1 = If this was not the case it would say so here
1.3.6.1.2.1.25.4.2.1.6.1 = 'application'
1.3.6.1.2.1.25.4.2.1.7.1 = 'running'
[2016-12-29 16:42:49,651-DEBUG]-(SNMPAgent) Read whole MIB (table walk)
1.3.6.1.2.1.25.4.2.1.1.1 = 1
1.3.6.1.2.1.25.4.2.1.2.1 = TradeLoader
1.3.6.1.2.1.25.4.2.1.3.1 = 0
1.3.6.1.2.1.25.4.2.1.4.1 = All is well
1.3.6.1.2.1.25.4.2.1.5.1 = If this was not the case it would say so here
1.3.6.1.2.1.25.4.2.1.6.1 = 'application'
1.3.6.1.2.1.25.4.2.1.7.1 = 'running'
1.3.6.1.2.1.25.5.1.1.1.1 = <no value>
1.3.6.1.2.1.25.5.1.1.2.1 = <no value>
[2016-12-29 16:42:53,490-DEBUG]-(SNMPAgent) done

Finally, the dispatcher is started.

The problem is that when I try and query the agent nothing happens. I get no response. I have looked at my code and one obvious thing about it is the fact that I do not explicitly link the snmpEngine to my created MIB. Should I do this?

Any insight would be greatly received as I'm struggling to understand where to go at the moment.

snmp mib pysnmp opennms
Original Q&A
2

There are 2 answers

0
Richard B On BEST ANSWER

I thought I would just post an answer to my question as it took me so long to figure out how to do what I need. Hopefully someone else will find this useful. The following code allows me to populate any MIB known to pysnmp and then make the MIB available to the network as an V2 SNMP Agent.

import logging

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

# Uncomment this to turn pysnmp debugging on
#debug.setLogger(debug.Debug('all'))

formatting = '[%(asctime)s-%(levelname)s]-(%(module)s) %(message)s'
logging.basicConfig(level=logging.DEBUG, format=formatting, )

logging.info("Starting....")

# Create SNMP engine
snmpEngine = engine.SnmpEngine()

# Transport setup

# UDP over IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTransport().openServerMode(('0.0.0.0', 12345))
)

# SNMPv2c setup

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

# Allow read MIB access for this user / securityModels at VACM
# Limit access to just the custom MIB. Widen if need be
config.addVacmUser(snmpEngine,
                   2,
                   'my-area',
                   'noAuthNoPriv',
                   (1, 3, 6, 1, 2, 1, 25, 4),
                   (1, 3, 6, 1, 2, 1, 25, 4))


# Create an SNMP context and ensure the custom MIB is loaded
# Your system must have this MIB installed otherwise pysnmp 
# can't load it! 
snmpContext = context.SnmpContext(snmpEngine)
logging.debug('Loading HOST-RESOURCES-MIB module...'),
mibBuilder = snmpContext.getMibInstrum().getMibBuilder()
mibBuilder.loadModules('HOST-RESOURCES-MIB')
mibInstrum = snmpContext.getMibInstrum()
logging.debug('done')

logging.debug('Building table entry index from human-friendly representation...')
# see http://www.oidview.com/mibs/0/HOST-RESOURCES-MIB.html
hostRunTable, = mibBuilder.importSymbols('HOST-RESOURCES-MIB', 'hrSWRunEntry')
instanceId = hostRunTable.getInstIdFromIndices(1)
logging.debug('done')


# The following shows the OID name mapping
#
# hrSWRunTable          1.3.6.1.2.1.25.4.2          <TABLE>
# hrSWRunEntry          1.3.6.1.2.1.25.4.2.1        <SEQUENCE>
# hrSWRunIndex          1.3.6.1.2.1.25.4.2.1.1      <Integer32>
# hrSWRunName           1.3.6.1.2.1.25.4.2.1.2      <InternationalDisplayString> 64 Char
# hrSWRunID             1.3.6.1.2.1.25.4.2.1.3      <ProductID>
# hrSWRunPath           1.3.6.1.2.1.25.4.2.1.4      <InternationalDisplayString> 128 octets
# hrSWRunParameters     1.3.6.1.2.1.25.4.2.1.5      <InternationalDisplayString> 128 octets
# hrSWRunType           1.3.6.1.2.1.25.4.2.1.6      <INTEGER>
# hrSWRunStatus         1.3.6.1.2.1.25.4.2.1.7      <INTEGER>  <<===== This is the key variable used by Opennms

# We are going to use OpenNMS as the SNMP manager. OpenNMS will poll this agent to check on its status. The manual 
# states:
#
# "This monitor tests the running state of one or more processes. It does this using SNMP and by inspecting the 
# hrSwRunTable of the HOST-RESOURCES-MIB. The test is done by matching a given process as hrSWRunName against
# the numeric value of the hrSWRunStatus". hrSWRunName is matched against the process name defined in the OpenNMS
# config file under the heading "service-name". hrSWRunStatus is set to whatever your desired status is. OpenNMS 
# will compare this value against the config file variable run-level. If hrSWRunStatus > run-level the process
# will be marked as having problems. for the complete page see: 
# http://docs.opennms.org/opennms/releases/18.0.1/guide-admin/guide-admin.html#_hostresourceswrunmonitor)


# I have made up an enterprise MIB for us. The number is moot as it's not going to go anywhere but the code needs 
# something valid.
# The enterprise MIB I have chosen is
enterpriseMib = (1, 3, 6, 1, 4, 1, 50000, 0)

logging.debug('Create/update HOST-RESOURCES-MIB::hrSWRunTable table row:')
varBinds = mibInstrum.writeVars((
                                 (hostRunTable.name + (1,) + instanceId, 1),
                                 (hostRunTable.name + (2,) + instanceId, 'TradeLoader'), # <=== Must match OpenNMS service-name variable
                                 (hostRunTable.name + (3,) + instanceId,  enterpriseMib), #  
                                 (hostRunTable.name + (4,) + instanceId, 'All is well'),
                                 (hostRunTable.name + (5,) + instanceId, 'If this was not the case it would say so here'),
                                 (hostRunTable.name + (6,) + instanceId, 4),# Values are ==> unknown(1), operatingSystem(2), deviceDriver(3), application(4)     
                                 (hostRunTable.name + (7,) + instanceId, 1) #<<=== This is the status number OpenNMS looks at Values are ==> running(1), runnable(2), notRunnable(3), invalid(4)
                                 ))

# --- end of  table population ---
logging.debug('Confirm that the data has been set by reading whole MIB (table walk)')
oid, val = (), None
while True:
    oid, val = mibInstrum.readNextVars(((oid, val),))[0]
    if exval.endOfMib.isSameTypeWith(val):
        break
    print('%s = %s' % ('.'.join([str(x) for x in oid]), val.prettyPrint()))
logging.debug('done')

# 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

The logger messages show

[2017-01-09 16:30:15,401-INFO]-(SNMPAgent) Starting.... [2017-01-09 16:30:15,490-DEBUG]-(SNMPAgent) Loading HOST-RESOURCES-MIB module... [2017-01-09 16:30:15,513-DEBUG]-(SNMPAgent) done [2017-01-09 16:30:15,513-DEBUG]-(SNMPAgent) Building table entry index from human-friendly representation... [2017-01-09 16:30:15,515-DEBUG]-(SNMPAgent) done [2017-01-09 16:30:15,515-DEBUG]-(SNMPAgent) Create/update HOST-RESOURCES-MIB::hrSWRunTable table row: [2017-01-09 16:30:15,536-DEBUG]-(SNMPAgent) Confirm that the data has been set by reading whole MIB (table walk)
1.3.6.1.2.1.25.4.2.1.1.1 = 1
1.3.6.1.2.1.25.4.2.1.2.1 = TradeLoader
1.3.6.1.2.1.25.4.2.1.3.1 = 1.3.6.1.4.1.50000.0
1.3.6.1.2.1.25.4.2.1.4.1 = All is well
1.3.6.1.2.1.25.4.2.1.5.1 = If this was not the case it would say so here
1.3.6.1.2.1.25.4.2.1.6.1 = 'application'
1.3.6.1.2.1.25.4.2.1.7.1 = 'running'
1.3.6.1.2.1.25.5.1.1.1.1 = <no value>
1.3.6.1.2.1.25.5.1.1.2.1 = <no value>
1.3.6.1.6.3.10.2.1.1.0 = 0x80004fb805049c06c8
1.3.6.1.6.3.10.2.1.2.0 = 2
1.3.6.1.6.3.10.2.1.3.0 = 0
1.3.6.1.6.3.10.2.1.4.0 = 65507
1.3.6.1.6.3.16.1.1.1.1.0 = 
1.3.6.1.6.3.16.1.2.1.1.2.7.109.121.45.97.114.101.97 = 2
1.3.6.1.6.3.16.1.2.1.2.2.7.109.121.45.97.114.101.97 = my-area
1.3.6.1.6.3.16.1.2.1.3.2.7.109.121.45.97.114.101.97 = v-1203634843-2
1.3.6.1.6.3.16.1.2.1.4.2.7.109.121.45.97.114.101.97 = 'nonVolatile'
1.3.6.1.6.3.16.1.2.1.5.2.7.109.121.45.97.114.101.97 = 'active'
1.3.6.1.6.3.16.1.4.1.1.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = 
1.3.6.1.6.3.16.1.4.1.2.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = 2
1.3.6.1.6.3.16.1.4.1.3.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = 'noAuthNoPriv'
1.3.6.1.6.3.16.1.4.1.4.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = 'exact'
1.3.6.1.6.3.16.1.4.1.5.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = rv-1203634843-2
1.3.6.1.6.3.16.1.4.1.6.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = wv-1203634843-2
1.3.6.1.6.3.16.1.4.1.7.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = nv-1203634843-2
1.3.6.1.6.3.16.1.4.1.8.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = 'nonVolatile'
1.3.6.1.6.3.16.1.4.1.9.14.118.45.49.50.48.51.54.51.52.56.52.51.45.50.0.2.1 = 'active'
1.3.6.1.6.3.16.1.5.2.1.1.15.114.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= rv-1203634843-2
1.3.6.1.6.3.16.1.5.2.1.1.15.119.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= wv-1203634843-2
1.3.6.1.6.3.16.1.5.2.1.2.15.114.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 1.3.6.1.2.1.25.4
1.3.6.1.6.3.16.1.5.2.1.2.15.119.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 1.3.6.1.2.1.25.4
1.3.6.1.6.3.16.1.5.2.1.3.15.114.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 
1.3.6.1.6.3.16.1.5.2.1.3.15.119.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 
1.3.6.1.6.3.16.1.5.2.1.4.15.114.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 'included'
1.3.6.1.6.3.16.1.5.2.1.4.15.119.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 'included'
1.3.6.1.6.3.16.1.5.2.1.5.15.114.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 'nonVolatile'
1.3.6.1.6.3.16.1.5.2.1.5.15.119.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 'nonVolatile'
1.3.6.1.6.3.16.1.5.2.1.6.15.114.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 'active'
1.3.6.1.6.3.16.1.5.2.1.6.15.119.118.45.49.50.48.51.54.51.52.56.52.51.45.50.11.1.3.6.1.2.1.25.4
= 'active'
1.3.6.1.6.3.18.1.1.1.1.109.121.45.97.114.101.97 = my-area
1.3.6.1.6.3.18.1.1.1.2.109.121.45.97.114.101.97 = public
1.3.6.1.6.3.18.1.1.1.3.109.121.45.97.114.101.97 = my-area
1.3.6.1.6.3.18.1.1.1.4.109.121.45.97.114.101.97 = 0x80004fb805049c06c8
1.3.6.1.6.3.18.1.1.1.5.109.121.45.97.114.101.97 = 
1.3.6.1.6.3.18.1.1.1.6.109.121.45.97.114.101.97 = 
1.3.6.1.6.3.18.1.1.1.7.109.121.45.97.114.101.97 = 'nonVolatile'
1.3.6.1.6.3.18.1.1.1.8.109.121.45.97.114.101.97 = 'active' [2017-01-09 16:30:15,683-DEBUG]-(SNMPAgent) done

And the agent can be queried to show get the results as follows:

snmpwalk -v 2c -c public -n my-context 0.0.0.0:12345 1.3.6

HOST-RESOURCES-MIB::hrSWRunIndex.1 = INTEGER: 1
HOST-RESOURCES-MIB::hrSWRunName.1 = STRING: "TradeLoader"
HOST-RESOURCES-MIB::hrSWRunID.1 = OID: SNMPv2-SMI::enterprises.50000.0
HOST-RESOURCES-MIB::hrSWRunPath.1 = STRING: "All is well"
HOST-RESOURCES-MIB::hrSWRunParameters.1 = STRING: "If this was not the case it would say so here"
HOST-RESOURCES-MIB::hrSWRunType.1 = INTEGER: application(4)
HOST-RESOURCES-MIB::hrSWRunStatus.1 = INTEGER: running(1)
HOST-RESOURCES-MIB::hrSWRunStatus.1 = No more variables left in this MIB View (It is past the end of the MIB tree)
2
Gambit Support On

You say

The problem is that when I try and query the agent nothing happens. I get no response

Looks like 2 problems:

a) localhost resolves to the loopback address 127.0.0.1 on my system, so that you can only access it from the same system as your agent.

b) you register as SNMP version 2 in addVacmUser so you cannot access with V1

After that:

% snmpwalk -v 2c -c public 127.0.0.1:12345
SNMPv2-MIB::sysDescr.0 = STRING: PySNMP engine version 4.3.2, Python 2.7.5 (default, Nov  3 2014, 14:33:39)  [GCC 4.8.3 20140911 (Red Hat 4.8.3-7)]
SNMPv2-MIB::sysObjectID.0 = OID: SNMPv2-SMI::enterprises.20408
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (1) 0:00:00.01
SNMPv2-MIB::sysContact.0 = STRING: 
...

although no HOST-RESOURCE-MIB objects. That is yet another problem.

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