What is 'my-creds', 'my-area', and 'my-router' in these Python PySNMP codes?

Question

I am new in using PySNMP module in Python. According to this user manual and this manual, the following python scripts perform similar things like the net-snmp command:

net-snmp v1 command:

snmpget -v1 -c public -ObentU 195.218.195.228 1.3.6.1.2.1.1.1.0

Python v1 script:

from twisted.internet import reactor, defer
from pysnmp.entity import engine, config
from pysnmp.entity.rfc3413.twisted import cmdgen
from pysnmp.carrier.twisted import dispatch
from pysnmp.carrier.twisted.dgram import udp

# Create SNMP engine instance
snmpEngine = engine.SnmpEngine()

# Instantiate and register Twisted dispatcher at SNMP engine
snmpEngine.registerTransportDispatcher(dispatch.TwistedDispatcher())

#
# SNMPv1 setup
#

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

# Specify security settings per SecurityName (SNMPv1 - 0, SNMPv2c - 1)
config.addTargetParams(snmpEngine, 'my-creds', 'my-area', 'noAuthNoPriv', 0)

#
# Setup transport endpoint and bind it with security settings yielding
# a target name
#

# UDP/IPv4
config.addSocketTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTwistedTransport().openClientMode()
)
config.addTargetAddr(
    snmpEngine, 'my-router',
    udp.domainName, ('195.218.195.228', 161),
    'my-creds'
)

# Error/response receiver
def cbFun(cbCtx):
    (errorIndication, errorStatus, errorIndex, varBinds) = cbCtx
    if errorIndication:
        print(errorIndication)
    # SNMPv1 response may contain noSuchName error *and* SNMPv2c exception,
    # so we ignore noSuchName error here
    elif errorStatus and errorStatus != 2:
        print('%s at %s' % (
                errorStatus.prettyPrint(),
                errorIndex and varBinds[int(errorIndex)-1][0] or '?'
            )
        )
    else:
        for oid, val in varBinds:
            print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))

    reactor.stop()

# Prepare request to be sent yielding Twisted deferred object
df = cmdgen.GetCommandGenerator().sendReq(
    snmpEngine,
    'my-router',
    ( ('1.3.6.1.2.1.1.1.0', None), ('1.3.6.1.2.1.1.2.0', None) ),
)

# Register error/response receiver function at deferred
df.addCallback(cbFun)

# Run Twisted main loop
reactor.run()

net-snmp v3 command:

snmpget -v3 -l authPriv -u usr-sha-aes -a SHA -A authkey1 -x AES -X privkey1 -ObentU 195.218.195.228:161  1.3.6.1.2.1.1.1.0

Python v3 script:

from twisted.internet import reactor, defer
from pysnmp.entity import engine, config
from pysnmp.entity.rfc3413.twisted import cmdgen
from pysnmp.carrier.twisted import dispatch
from pysnmp.carrier.twisted.dgram import udp

# Create SNMP engine instance
snmpEngine = engine.SnmpEngine()

# Instantiate and register Twisted dispatcher at SNMP engine
snmpEngine.registerTransportDispatcher(dispatch.TwistedDispatcher())

#
# SNMPv3/USM setup
#

# user: usr-sha-aes, auth: SHA, priv AES
config.addV3User(
    snmpEngine, 'usr-sha-aes',
        config.usmHMACSHAAuthProtocol, 'authkey1',
            config.usmAesCfb128Protocol, 'privkey1'
            )
config.addTargetParams(snmpEngine, 'my-creds', 'usr-sha-aes', 'authPriv')

#
# Setup transport endpoint and bind it with security settings yielding
# a target name
#

# UDP/IPv4
config.addSocketTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTwistedTransport().openClientMode()
)
config.addTargetAddr(
    snmpEngine, 'my-router',
    udp.domainName, ('195.218.195.228', 161),
    'my-creds'
)

# Error/response receiver
def cbFun(cbCtx):
    (errorIndication, errorStatus, errorIndex, varBinds) = cbCtx
    if errorIndication:
        print(errorIndication)
    elif errorStatus:
        print('%s at %s' % (
                errorStatus.prettyPrint(),
                errorIndex and varBinds[int(errorIndex)-1][0] or '?'
            )
        )
    else:
        for oid, val in varBinds:
            print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))

    reactor.stop()

# Prepare request to be sent yielding Twisted deferred object
df = cmdgen.GetCommandGenerator().sendReq(
    snmpEngine,
    'my-router',
    ( ('1.3.6.1.2.1.1.1.0', None), ),
)

# Register error/response receiver function at deferred
df.addCallback(cbFun)

# Run Twisted main loop
reactor.run()

In the above net-snmp commands, you can see that there is no 'my-creds', 'my-area', and 'my-router' parameters. However, these parameters are used in the Python scripts.

May I know what is 'my-creds', 'my-area', and 'my-router' in these Python PySNMP scripts?

Maybe read pysnmp docs or ask developers. – furas Jul 09 '14 at 16:46 — furas, Jul 09 '14 at 16:46

score 3 · Accepted Answer · answered Jul 09 '14 at 19:46

In SNMP (not just pysnmp), system configuration is scattered across several 'SNMP tables'. They are defined in their respective MIBs and their rows can be logically linked one with the other by columnar names.

In the end you can refer to all SNMP configuration details for a particular SNMP peer via a single ID. Also, you can re-use common parts of SNMP configuration for multiple distinct peers.

In most pysnmp scripts you can spot the following tables and their relations:

securityName + securityLevel + snmpMessageProcessingModel (3) -> snmpTargetParameters (see SNMP-TARGET-MIB::snmpTargetParams)
securityName + communityName + snmpMessageVersion (1|2c) -> snmpTargetParameters (see SNMP-COMMUNITY-MIB::snmpCommunity)
snmpTargetParameters + targetAddress + timeout + retries -> snmpTarget (see SNMP-TARGET-MIB::snmpTargetAddr)

So snmpTarget (e.g. 'my-router') is the top-level ID that can be referred to when requesting SNMP application (like Command Generator) to send SNMP request to specific peer via specific SNMP version and with specific credentials.

One of the features of this configuration model (for at least for SNMP Agent situation) is that it can be managed remotely through SNMP.

What is 'my-creds', 'my-area', and 'my-router' in these Python PySNMP codes?

1 Answers1