How to make a single GETNEXT query in PySNMP

Question

I'm trying to make a simple snmp GETNEXT query to retrieve only the next item of given OID in tree hierarchy.

For example, what I want is:

When i make a GETNEXT request with OID 1.3.6.1.2.1.1 (iso.org.dod.internet.mgmt.mib-2.system)

I expect to get a single response including OID 1.3.6.1.2.1.1.1.0 (iso.org.dod.internet.mgmt.mib-2.system.sysDescr.0) with its corresponding value.

The fact is:

Insted of retrieving single next value, PySNMP performs an SNMP walk under 1.3.6.1.2.1.1 and retrieves all subItems.

How can i change this behaviour and make it to just return single next value instead of performing an snmpwalk?

I use the below code which is taken from PySNMP's documentation.

# GETNEXT Command Generator
from pysnmp.entity.rfc3413.oneliner import cmdgen

errorIndication, errorStatus, errorIndex, \
                 varBindTable = cmdgen.CommandGenerator().nextCmd(
    cmdgen.CommunityData('test-agent', 'public'),
    cmdgen.UdpTransportTarget(('localhost', 161)),
    (1,3,6,1,2,1,1)
    )

if errorIndication:
    print errorIndication
else:
    if errorStatus:
        print '%s at %s\n' % (
            errorStatus.prettyPrint(),
            errorIndex and varBindTable[-1][int(errorIndex)-1] or '?'
            )
    else:
        for varBindTableRow in varBindTable:
            for name, val in varBindTableRow:
                print '%s = %s' % (name.prettyPrint(), val.prettyPrint())

Answer 1

@Cankut, pysnmp's "oneliner" GETNEXT API works by retrieving either all OIDs under a given prefix or all OIDs till end-of-mib.

One way of doing what you want would be to replace pysnmp's stock response processing function with your own (that would also require using a bit lower-level async API):

from pysnmp.entity.rfc3413.oneliner import cmdgen

def cbFun(sendRequestHandle, errorIndication, errorStatus, errorIndex,
          varBindTable, cbCtx):
    if errorIndication:
        print(errorIndication)
        return 1
    if errorStatus:
        print(errorStatus.prettyPrint())
        return 1
    for varBindRow in varBindTable:
        for oid, val in varBindRow:
            print('%s = %s' % (oid.prettyPrint(),
                               val and val.prettyPrint() or '?'))

cmdGen  = cmdgen.AsynCommandGenerator()

cmdGen.nextCmd(
    cmdgen.CommunityData('test-agent', 'public'),
    cmdgen.UdpTransportTarget(('localhost', 161)),
    ((1,3,6,1,2,1,1),),
    (cbFun, None)
)

cmdGen.snmpEngine.transportDispatcher.runDispatcher()

Answer 2

errorIndication, errorStatus, errorIndex, \
                 varBindTable = cmdgen.CommandGenerator().nextCmd(
    cmdgen.CommunityData('test-agent', 'public'),
    cmdgen.UdpTransportTarget(('localhost', 161)),
    (1,3,6,1,2,1,1),maxRows=1
    )