snmpwalk with PySNMP

Question

I’d like to reproduce the comportment of the following SNMP command :

snmpwalk -v2c -cpublic 192.168.0.10 1.3.6.1.2.1.25.2.3.1.3

which gives me this output :

iso.3.6.1.2.1.25.2.3.1.3.1 = STRING: "Physical memory"
iso.3.6.1.2.1.25.2.3.1.3.3 = STRING: "Virtual memory"
iso.3.6.1.2.1.25.2.3.1.3.6 = STRING: "Memory buffers"
iso.3.6.1.2.1.25.2.3.1.3.7 = STRING: "Cached memory"
iso.3.6.1.2.1.25.2.3.1.3.8 = STRING: "Shared memory"
iso.3.6.1.2.1.25.2.3.1.3.10 = STRING: "Swap space"
iso.3.6.1.2.1.25.2.3.1.3.31 = STRING: "/"
iso.3.6.1.2.1.25.2.3.1.3.37 = STRING: "/run"
iso.3.6.1.2.1.25.2.3.1.3.39 = STRING: "/dev/shm"
iso.3.6.1.2.1.25.2.3.1.3.40 = STRING: "/run/lock"
iso.3.6.1.2.1.25.2.3.1.3.41 = STRING: "/sys/fs/cgroup"
iso.3.6.1.2.1.25.2.3.1.3.59 = STRING: "/tmp"
iso.3.6.1.2.1.25.2.3.1.3.60 = STRING: "/run/cgmanager/fs"
iso.3.6.1.2.1.25.2.3.1.3.61 = STRING: "/run/user/112"
iso.3.6.1.2.1.25.2.3.1.3.63 = STRING: "/run/user/0"

So I tried this code :

#!/usr/bin/env python3
from pysnmp.hlapi import *

def walk(host, oid):
    for (errorIndication,errorStatus,errorIndex,varBinds) in nextCmd(SnmpEngine(), 
        CommunityData('public'), UdpTransportTarget((host, 161)), ContextData(), 
        ObjectType(ObjectIdentity(oid))):
        if errorIndication:
            print(errorIndication, file=sys.stderr)
            break
        elif errorStatus:
            print('%s at %s' % (errorStatus.prettyPrint(),
                                errorIndex and varBinds[int(errorIndex) - 1][0] or '?'), 
                                file=sys.stderr)             
            break
        else:
            for varBind in varBinds:
                print(varBind)

walk('192.168.0.10','1.3.6.1.2.1.25.2.3.1.3')

and the problem is that it returns a lot of unwanted OIDs…

I tried different things, like using the getCmd() function but I can’t manage to have it working the way I want.

I could call the external snmpwalk command from my Python code but I’d prefer to find a solution using the Python module.

Any idea to help me?

Solution

Try passing the lexicographicMode keyword argument to the nextCmd(). For example:

for (errorIndication,
     errorStatus,
     errorIndex,
     varBinds) in nextCmd(SnmpEngine(), 
                          CommunityData('public'),
                          UdpTransportTarget((host, 161)),
                          ContextData(),                                                           
                          ObjectType(ObjectIdentity(oid)),
                          lexicographicMode=False):
    ...

That should have the effect of capping the SNMP walk by the initial OID you give it (assuming that unwanted OIDs you mention are those going out of the prefix).