CODEWITHSUNDEEP
pythonnet-snmppysnmp
jcoppens
jcoppens

Reputation: 5440

Using SNMP, trying to get to the data in a TP-LINK modem

The other day, a modem broke down, and I acquired a new TP-LINK TD8816 to replace it. I've been trying to get my feet wet in SNMP to get at the modem stats. Here are the steps I took:

When I try to access variables in the adslMIB, none are found:

Using mbrowse I see many declared variables, but 'get' tells me the variable doesn't exit. The (modified) pysnmp 'one-liner' demo program produces an error (see below).

I can access sysDescr and OID in the modem:

$ snmpwalk -Os -c public -v 1 10.0.0.2 1.3.6.1.2.1.1.1 
sysDescr.0 = STRING: TD-8816
$ snmpwalk -Os -c public -v 1 10.0.0.2 1.3.6.1.2.1.1.2
sysObjectID.0 = OID: enterprises.1.2.3.4.5

but nothing else...

This is the modified pysnmb script:

from pysnmp.entity.rfc3413.oneliner import cmdgen
from pysnmp import debug

class SNMP_access():
    def __init__(self):
        self.cmdGen = cmdgen.CommandGenerator()

    def test(self):
        errorIndication, errorStatus, errorIndex, varBinds = \
            self.cmdGen.getCmd(
                cmdgen.CommunityData('public'),
                cmdgen.UdpTransportTarget(('10.0.0.2', 161)),
                cmdgen.MibVariable('ADSL-LINE-MIB', 'adslAturPerfLoss', '0')
            )

        # Check for errors and print out results
        if errorIndication:
            print(errorIndication)
        else:
            if errorStatus:
                print('%s at %s' % (
                    errorStatus.prettyPrint(),
                    errorIndex and varBinds[int(errorIndex)-1] or '?'
                    )
                )
            else:
                for name, val in varBinds:
                    print('%s = %s' % (name.prettyPrint(), val.prettyPrint()))

def main():
    # use specific flags or 'all' for full debugging
    #debug.setLogger(debug.Debug('dsp', 'msgproc', 'secmode'))

    snmp = SNMP_access()
    snmp.test()
    return 0

if __name__ == '__main__':
    main()

and the resulting traceback:

Traceback (most recent call last):
  File "snmptest.py", line 63, in <module>
    main()
  File "snmptest.py", line 59, in main
    snmp.test()
  File "snmptest.py", line 37, in test
    cmdgen.MibVariable('ADSL-LINE-MIB', 'adslAturPerfLoss', '0')
  File "/usr/lib64/python2.7/site-packages/pysnmp-4.2.5-py2.7.egg/pysnmp/entity/rfc3413/oneliner/cmdgen.py", line 424, in getCmd
    kwargs.get('contextName', null)
  File "/usr/lib64/python2.7/site-packages/pysnmp-4.2.5-py2.7.egg/pysnmp/entity/rfc3413/oneliner/cmdgen.py", line 277, in getCmd
    self.makeReadVarBinds(varNames),
  File "/usr/lib64/python2.7/site-packages/pysnmp-4.2.5-py2.7.egg/pysnmp/entity/rfc3413/oneliner/cmdgen.py", line 201, in makeReadVarBinds
    [ (x, self._null) for x in varNames ], oidOnly=True
  File "/usr/lib64/python2.7/site-packages/pysnmp-4.2.5-py2.7.egg/pysnmp/entity/rfc3413/oneliner/cmdgen.py", line 209, in makeVarBinds
    varName.resolveWithMib(self.mibViewController, oidOnly=True)
  File "/usr/lib64/python2.7/site-packages/pysnmp-4.2.5-py2.7.egg/pysnmp/entity/rfc3413/oneliner/mibvar.py", line 180, in resolveWithMib
    instIds = rowNode.getInstIdFromIndices(*self.__args[2:])
  File "/usr/lib64/python2.7/site-packages/pysnmp-4.2.5-py2.7.egg/pysnmp/smi/mibs/SNMPv2-SMI.py", line 1096, in getInstIdFromIndices
    mibObj.syntax.clone(indices[idx]), impliedFlag
  File "/usr/lib64/python2.7/site-packages/pyasn1-0.1.7-py2.7.egg/pyasn1/type/univ.py", line 107, in clone
    return self.__class__(value, tagSet, subtypeSpec, namedValues)
  File "/usr/lib64/python2.7/site-packages/pyasn1-0.1.7-py2.7.egg/pyasn1/type/univ.py", line 22, in __init__
    self, value, tagSet, subtypeSpec
  File "/usr/lib64/python2.7/site-packages/pyasn1-0.1.7-py2.7.egg/pyasn1/type/base.py", line 69, in __init__
    self._verifySubtypeSpec(value)
  File "/usr/lib64/python2.7/site-packages/pyasn1-0.1.7-py2.7.egg/pyasn1/type/base.py", line 33, in _verifySubtypeSpec
    raise c('%s at %s' % (i, self.__class__.__name__))
pyasn1.type.error.ValueConstraintError: ConstraintsIntersection(ConstraintsIntersection(ConstraintsIntersection(), ValueRangeConstraint(-2147483648, 2147483647)), ValueRangeConstraint(1, 2147483647)) failed at: "ValueRangeConstraint(1, 2147483647) failed at: "0"" at InterfaceIndex

EDIT: Some more details, in response to Ilya's reply:

Upvotes: 0

Views: 3457

Answers (1)

Ilya Etingof
Ilya Etingof

Reputation: 5555

This particular SNMP error occurs because you are trying to build an OID with invalid SNMP table index.

The adslAturPerfLoss table column belongs to adslAturPerfDataEntry which uses ifIndex object for indexing table objects. The ifIndex column has InterfaceIndex for value type which, in turn, is an Integer constrained to 1..2147483647 values. You are giving it 0 what produces an error.

However this does not explain why your modem does not show you most of its SNMP variables. Things to check related to your modem:

  • Does vendor offer ADSL-MIB support?
  • Whether vendor requires some specific SNMP view configuration of modem's SNMP Agent to let you access other OIDs?
  • Maybe SNMP Agent inside the modem works differently over SNMP v2c?
  • ..or when using some other SNMP community name?
  • ..or when querying some other network interface (if there are others)?
  • ..or when the modem is fully operational (e.g. connected to its peer)?

Upvotes: 1

Related Questions