SNMP SET request using Python

Question

I need to controle a simple device via SNMP using Python 3.7 just to get it "ON" (1) and "OFF" (0). In the device manual, in the MIB information, there is a list of OID for each command (ex : GET output statue : 1.3.6........).

I manage to have the GET request working as I like (source : http://snmplabs.com/pysnmp/examples/hlapi/asyncore/sync/manager/cmdgen/snmp-versions.html ) :

from pysnmp.hlapi import *

    g = getCmd(SnmpEngine()
              , CommunityData('public', mpModel=1)
              , hlapi.UdpTransportTarget(('DEVICE IP', 161))
              , ContextData()
              , ObjectType(ObjectIdentity('GET OID given by the device manual')))

    errorIndication, errorStatus, errorIndex, varBinds = next(g)

    for varBind in varBinds:
        print(' = '.join([x.prettyPrint() for x in varBind]))

However when I try to use SET the same way : (source : http://snmplabs.com/pysnmp/examples/hlapi/asyncore/sync/manager/cmdgen/modifying-variables.html )

from pysnmp.hlapi import *
g = setCmd(SnmpEngine()
           , CommunityData('public', mpModel=1)
           , hlapi.UdpTransportTarget(('DEVICE IP', 161))
           , ContextData()
           , ObjectType(ObjectIdentity('SET OID given by the device manual, which is the same as the GET'), '1') #1 = new value
           )

errorIndication, errorStatus, errorIndex, varBinds = next(g)

print(errorIndication, varBinds)

I get the following error :

MibNotFoundError: SET OID compilation error(s): missingcaused by <class 'pysnmp.smi.error.MibNotFoundError'>: MIB file "SET OID.py[co]" not found in search path (DirMibSource('/home/username/anaconda3/lib/python3.7/site-packages/pysnmp/smi/mibs'), DirMibSource('/home/username/anaconda3/lib/python3.7/site-packages/pysnmp/smi/mibs/instances'), DirMibSource('pysnmp_mibs'), DirMibSource('/home/username/.pysnmp/mibs'))

I don't understand why it works without problem in one case and not in the other. In the device manual the instruction is the same as GET but there is STRING 0 or 1 at the end, I guess I'm missing something here but I can't found how to write it.

I just want to give this very simple instruction, if someone has an easy answer or alternative.

Thank you very much

PS : I also tried this tutorial ( https://www.ictshore.com/sdn/python-snmp-tutorial/ ) which make it's own functions, and again GET works but not SET. I got that my OID is not Object-TYPE.

Answer 1

When you pass a value to setCMD() it (apparently) has to be a pysnmp.hlapi object type. For example:

from pysnmp.hlapi import *
engine = SnmpEngine()
community = CommunityData('public', mpModel=1)
transport = UdpTransportTarget(('192.168.1.1', 161))
context = ContextData()

# Your OID goes here.
identity = ObjectIdentity('1.3.6.1.4.1.534.6.6.7.6.1.1.3.0')

# If this was a string value, use OctetString() instead of Integer().
new_value = Integer(1)
type = ObjectType(identity, new_value)

# Setting lookupMib=False here because this example uses a numeric OID.
g = setCmd(engine, community, transport, context, identity, type, lookupMib=False)

errorIndication, errorStatus, errorIndex, varBinds = next(g)
print(errorIndication, varBinds)

It's possible that I'm missing a subtlety of how to use pysnmp.hlapi , but this is the incantation that worked for me.