How to get data from SNMP with python?

Question

How to get value mac and vlan from fdb table uses python?
In bash snmpwalk work fine:

snmpwalk -v2c -c pub 192.168.0.100 1.3.6.1.2.1.17.7.1.2.2.1.2

pysnmp:

import os, sys
import socket
import random
from struct import pack, unpack
from datetime import datetime as dt

from pysnmp.entity.rfc3413.oneliner import cmdgen
from pysnmp.proto.rfc1902 import Integer, IpAddress, OctetString

ip='192.168.0.100'
community='pub'
value=(1,3,6,1,2,1,17,7,1,2,2,1,2)

generator = cmdgen.CommandGenerator()
comm_data = cmdgen.CommunityData('server', community, 1) # 1 means version SNMP v2c
transport = cmdgen.UdpTransportTarget((ip, 161))

real_fun = getattr(generator, 'getCmd')
res = (errorIndication, errorStatus, errorIndex, varBinds)\
    = real_fun(comm_data, transport, value)

if not errorIndication is None  or errorStatus is True:
       print "Error: %s %s %s %s" % res
else:
       print "%s" % varBinds

output: [(ObjectName(1.3.6.1.2.1.17.7.1.2.2.1.2), NoSuchInstance(''))]

import netsnmp

def getmac():
    oid = netsnmp.VarList(netsnmp.Varbind('.1.3.6.1.2.1.17.7.1.2.2.1.2'))
    res = netsnmp.snmpgetbulk(oid, Version = 2, DestHost='192.168.0.100',
                           Community='pub')
    return res

print getmac()

output: ('27', '27', '25', '27', '27', '27', '24', '27', '25', '18', '4', '27', '25', '27', '27', '25', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '23', '25', '27', '27', '27', '25', '27', '25', '27', '27', '25', '27', '27', '27', '27', '27', '27', '27', '27', '27', '25', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '25', '25', '25', '7', '27', '27', '9', '25', '27', '20', '19', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '11', '25', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '27', '25', '27', '27', '27', '27', '27', '27', '27', '27', '27', '2', '27', '5', '27', '0', '27', '27', '27', '27', '27')

Firs script(pysnmp) return NoSuchInstance. Second script(netsnmp) return list of ports but without mac and vlan. What wrong?

Solution

In the pysnmp example you are doing an SNMPGET (snmpget), not a GETNEXT (snmpwalk). If you change,

real_fun = getattr(generator, 'getCmd')

to

real_fun = getattr(generator, 'nextCmd')

you will start to see useful results.

As for the discrepancy you saw in the results between snmpwalk and the python net-snmp bindings result: snmpwalk and snmpbulkget behave differently. If you do an snmpbulkget from the command line with the same options as the snmpwalk you'll receive the same results as your python net-snmp example.

If you update the following line in your python net-snmp example,

res = netsnmp.snmpgetbulk(oid, Version=2, DestHost='192.168.0.100', 
                          Community='pub')

to

res = netsnmp.snmpwalk(oid, Version=2, DestHost='192.168.0.100', 
                       Community='pub')

then you should now get the same list of results from the python net-snmp example as you see when you do an snmpwalk on the command line.