contextName failing. V3 to cisco switch

[gittyhubbyfrankybobby]

this snmpwalk command succeeds using context "vlan-10" snmpwalk -v3 -l authPriv -u username -a SHA -A asdfasdfasdf -x DES -X asdfasdfasdf -n vlan-10 10.10.255.7 .1.3.6.1.2.1.17.4.3.1.1

But this code comes up with this error

SNMPv2-SMI::mib-2.17.4.3.1.1 = No Such Instance currently exists at this OID

from pysnmp.hlapi import *
from pysnmp.entity.rfc3413.oneliner import cmdgen

macoid  = '.1.3.6.1.2.1.17.4.3.1.1'

errorIndication, errorStatus, errorIndex, varBinds = next(
    getCmd(SnmpEngine(),
           UsmUserData('username', 'asdfasdfasdf', 'asdfasdfasdf',
                       authProtocol=usmHMACSHAAuthProtocol,
                       privProtocol=usmDESPrivProtocol),
           UdpTransportTarget(('10.10.255.7', 161)),
           ContextData(contextName='vlan-10'),
           ObjectType(ObjectIdentity(macoid)))
)

if errorIndication:
    print(errorIndication)
elif errorStatus:
    print('%s at %s' % (errorStatus.prettyPrint(),
                        errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
else:
    for varBind in varBinds:
        print(' = '.join([x.prettyPrint() for x in varBind]))

[etingof]

One thing is that with pysnmp you are using SNMP GET, while with snmpwalk you do SNMP GETNEXT. That can cause the error you observe.

Otherwise, I'd suggest taking a look at what goes to the wire with tcpdump.

[gittyhubbyfrankybobby]

i changed it to:

from pysnmp.hlapi import *
from pysnmp.entity.rfc3413.oneliner import cmdgen

macoid  = '.1.3.6.1.2.1.17.4.3.1.1'

errorIndication, errorStatus, errorIndex, varBinds = next(
    nextCmd(SnmpEngine(),
           UsmUserData('username', 'asdfasdfasdf', 'asdfasdfasdf',
                       authProtocol=usmHMACSHAAuthProtocol,
                       privProtocol=usmDESPrivProtocol),
           UdpTransportTarget(('10.10.255.7', 161)),
           ContextData(contextName='vlan-10'),
           ObjectType(ObjectIdentity(macoid)))
)

if errorIndication:
    print(errorIndication)
elif errorStatus:
    print('%s at %s' % (errorStatus.prettyPrint(),
                        errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
else:
    for varBind in varBinds:
        print(' = '.join([x.prettyPrint() for x in varBind]))

and I get the output of 1.3.6.1.6.3.11.2.1.3.0 or

>>> varBind
ObjectType(ObjectIdentity(<ObjectName value object at 0x7f602f5e06a0 tagSet <TagSet object at 0x7f6034907390 tags 0:0:6> payload [1.3.6.1.2.1.17.4.3.1.1]>), <NoSuchInstance value object at 0x7f602f5e0780 tagSet <TagSet object at 0x7f603487e6d8 tags 128:0:1> subtypeSpec <ConstraintsIntersection object at 0x7f60349072e8 consts <SingleValueConstraint object at 0x7f6034907208 consts b''>> encoding iso-8859-1 payload [No Such Instance...ists at this OID]>)

I'll see if I can do a tcpdump.

[gittyhubbyfrankybobby]

I got it settled with a variant of this

for (errorIndication,
     errorStatus,
     errorIndex,
     varBinds) in nextCmd(SnmpEngine(),
           UsmUserData('username', 'xxxxxxxx', 'xxxxxxxxxxx',
           authProtocol=usmHMACSHAAuthProtocol,
           privProtocol=usmDESPrivProtocol),
           UdpTransportTarget(('10.10.10.10', 161)),
           ContextData(contextName='vlan-10'),
           ObjectType(ObjectIdentity('.1.3.6.1.2.1.17.4.3.1.1')),
           lexicographicMode=False):
    if errorIndication:
        print(errorIndication)
        break
    elif errorStatus:
        print('%s at %s' % (errorStatus.prettyPrint(),
                            errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
        break
    else:
        for varBind in varBinds:
            print(' = '.join([x.prettyPrint() for x in varBind]))

[etingof]

In your version two, I do not understand how you could possibly get no-such-instance response. That should not happen with nextCmd.

Anyway, glad it works now! \o/