Agent side#

Implementing MIB objects#

This script explains how SNMP Agent application could model real-world data as Managed Objects defined in MIB.

from pysnmp.smi import builder

# MIB Builder is normally pre-created by SNMP engine
mibBuilder = builder.MibBuilder()

#
# This may be done in a stand-alone file and then loaded up
# by SNMP Agent
#

# A base class for a custom Managed Object
(MibScalarInstance,) = mibBuilder.importSymbols("SNMPv2-SMI", "MibScalarInstance")

# Managed object specification
(sysLocation,) = mibBuilder.importSymbols("SNMPv2-MIB", "sysLocation")


# Custom Managed Object
class MySysLocationInstance(MibScalarInstance):
    # noinspection PyUnusedLocal
    def readGet(self, varBind, **context):
        # Just return a custom value
        return varBind[0], self.syntax.clone("The Leaky Cauldron")


sysLocationInstance = MySysLocationInstance(sysLocation.name, (0,), sysLocation.syntax)

# Register Managed Object with a MIB tree
mibBuilder.exportSymbols(
    # '__' prefixed MIB modules take precedence on indexing
    "__MY-LOCATION-MIB",
    sysLocationInstance=sysLocationInstance,
)

if __name__ == "__main__":
    #
    # This is what is done internally by Agent.
    #
    from pysnmp.smi import instrum, exval

    mibInstrum = instrum.MibInstrumController(mibBuilder)

    print("Remote manager read access to MIB instrumentation (table walk)")

    varBinds = [((), None)]

    while True:
        varBinds = mibInstrum.readNextVars(*varBinds)
        oid, val = varBinds[0]
        if exval.endOfMib.isSameTypeWith(val):
            break
        print(oid, val.prettyPrint())

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Agent operations on MIB#

This script explains how SNMP Agent application manipulates its MIB possibly triggered by SNMP Manager’s commands.

# SNMP agent backend e.g. Agent access to Managed Objects
from pysnmp.smi import builder, instrum, exval

print("Loading MIB modules..."),
mibBuilder = builder.MibBuilder().loadModules(
    "SNMPv2-MIB", "SNMP-FRAMEWORK-MIB", "SNMP-COMMUNITY-MIB"
)
print("done")

print("Building MIB tree..."),
mibInstrum = instrum.MibInstrumController(mibBuilder)
print("done")

print("Building table entry index from human-friendly representation..."),
(snmpCommunityEntry,) = mibBuilder.importSymbols(
    "SNMP-COMMUNITY-MIB", "snmpCommunityEntry"
)
instanceId = snmpCommunityEntry.getInstIdFromIndices("my-router")
print("done")

print("Create/update SNMP-COMMUNITY-MIB::snmpCommunityEntry table row: ")
varBinds = mibInstrum.writeVars(
    (snmpCommunityEntry.name + (2,) + instanceId, "mycomm"),
    (snmpCommunityEntry.name + (3,) + instanceId, "mynmsname"),
    (snmpCommunityEntry.name + (7,) + instanceId, "volatile"),
)
for oid, val in varBinds:
    print(
        "{} = {}".format(
            ".".join([str(x) for x in oid]),
            not val.isValue and "N/A" or val.prettyPrint(),
        )
    )
print("done")

print("Read whole MIB (table walk)")
varBinds = [((), None)]
while True:
    varBinds = mibInstrum.readNextVars(*varBinds)
    oid, val = varBinds[0]
    if exval.endOfMib.isSameTypeWith(val):
        break
    print(
        "{} = {}".format(
            ".".join([str(x) for x in oid]),
            not val.isValue and "N/A" or val.prettyPrint(),
        )
    )
print("done")

print("Unloading MIB modules..."),
mibBuilder.unloadModules()
print("done")

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