Using PySNMP as Trap Receiver with own/vendor MIB

Question

I try to use PySNMP to receive SNMPv3 Traps. I found this example code:

#!/usr/bin/env /usr/bin/python3

from pysnmp.entity import engine, config
from pysnmp.carrier.asyncore.dgram import udp
from pysnmp.entity.rfc3413 import ntfrcv
from pysnmp.proto.api import v2c
from pysnmp.smi.rfc1902 import ObjectIdentity

snmpEngine = engine.SnmpEngine()

# Transport setup

# UDP over IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTransport().openServerMode(('0.0.0.0', 162)),
)

# SNMPv3/USM setup
config.addV3User(
    snmpEngine, '<username>',
    config.usmHMACMD5AuthProtocol, '<password>',
    config.usmAesCfb128Protocol, '<password>',
    securityEngineId=v2c.OctetString(hexValue='<engineid>')
)

def cbFun(snmpEngine, stateReference, contextEngineId, contextName,
          varBinds, cbCtx):
    print('Notification from ContextEngineId "%s", ContextName "%s"' (contextEngineId.prettyPrint(), contextName.prettyPrint()))
    for name, val in varBinds:
        print('%s = %s' % (name.prettyPrint(), val.prettyPrint()))

# Register SNMP Application at the SNMP engine
ntfrcv.NotificationReceiver(snmpEngine, cbFun)

snmpEngine.transportDispatcher.jobStarted(1)  # this job would never finish

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

This code works for me, but i get the raw Traps. I have an vendor specific MIB File I want to use. But I can't find any documentation how to bind the mib to the snmpEngine. The examples using MIBs from the PySNMP documentation show only the usage for SNMP GET operations and are not applicable here. Has someone tried this before and can help me?

Thanks!

Answer 1

If your goal is to resolve raw variable-bindings you receive into human-friendly form, then you need to process those variable-bindings through the MIB browser object.

You are right, that's exactly the same operation that command generator frequently performs in the examples.

from pysnmp.smi import builder, view, compiler, rfc1902

# Assemble MIB browser
mibBuilder = builder.MibBuilder()
mibViewController = view.MibViewController(mibBuilder)
compiler.addMibCompiler(
    mibBuilder, sources=['file:///usr/share/snmp/mibs',
                         'http://mibs.snmplabs.com/asn1/@mib@'])

# Pre-load MIB modules that define objects we receive in TRAPs
mibBuilder.loadModules('SNMPv2-MIB', 'SNMP-COMMUNITY-MIB')

# This is what we would get in a TRAP PDU
varBinds = [
    ('1.3.6.1.2.1.1.3.0', 12345),
    ('1.3.6.1.6.3.1.1.4.1.0', '1.3.6.1.6.3.1.1.5.2'),
    ('1.3.6.1.6.3.18.1.3.0', '0.0.0.0'),
    ('1.3.6.1.6.3.18.1.4.0', ''),
    ('1.3.6.1.6.3.1.1.4.3.0', '1.3.6.1.4.1.20408.4.1.1.2'),
    ('1.3.6.1.2.1.1.1.0', 'my system')
]

# Pass raw var-binds through MIB browser
varBinds = [
    rfc1902.ObjectType(rfc1902.ObjectIdentity(x[0]), x[1]).resolveWithMib(mibViewController)
    for x in varBinds
]

for varBind in varBinds:
    print(varBind.prettyPrint())