PySNMP - default location of the compiled MIBs - pysnmp

Question

I configured the compiler where to look for asn1 MIBs as follows:
compiler.addMibCompiler(mibBuilder, sources=['/usr/share/snmp/mibs'])
Then used getCmd() as:
errorIndication, errorStatus, errorIndex, varBinds = next(
getCmd(SnmpEngine(),
CommunityData('private', mpModel=0),
UdpTransportTarget(('192.168.56.20', '161')),
ContextData(),
ObjectType(ObjectIdentity('VLAN-MIB','InterfaceMode',3))))
I find VLAN-MIB.py in $HOME/.pysnmp/mibs and everything worked fine.
But I wanted to modify the asn1 MIBs location to my local folder. Say:
/home/krish/mibs
I tried it in 2 different ways:
This:
compiler.addMibCompiler(mibBuilder, sources=['/home/krish/mibs'])`
This:
errorIndication, errorStatus, errorIndex, varBinds = next(
getCmd(SnmpEngine(),
CommunityData('private', mpModel=0),
UdpTransportTarget(('192.168.56.20', '161')),
ContextData(),
ObjectType(ObjectIdentity('VLAN-MIB','InterfaceMode',3).addAsn1MibSource('/home/krish/mibs')))
)
Either way, I am getting error which says that VLAN-MIB could not be found.
But if I compile it myself offline and place the VLAN-MIB.py file in the specified directory as:
errorIndication, errorStatus, errorIndex, varBinds = next(
getCmd(SnmpEngine(),
CommunityData('private', mpModel=0),
UdpTransportTarget(('192.168.56.20', '161')),
ContextData(),
ObjectType(ObjectIdentity('VLAN-MIB','InterfaceMode',3).addMibSource('/home/krish/mibs')))
)
it worked fine.
So my question is where the compiled MIBs (.py) are placed after PySMI is automatically parses the asn1 MIBs? I did not find them in default location $HOME/.pysnmp/mibs in the above case.
and how do I tell pysnmp/pysmi where to keep the auto-generated .py file.
and I don't want to use addMibSource() in every get/set calls. addMibCompiler() worked fine only for the /usr/share/snmp/mibs, not for the user directories.
Wondering what I am missing here. Appreciate help.

Answer 1

My guesses are:
It is that ASN.1 MIB could not be found, not its compiled counterpart VLAN-MIB.py
It is not that ASN.1 VLAN-MIB could not be found, but some other ASN.1 MIB on which VLAN-MIB is dependent
What exactly pysnmp error says?
Since you work with ASN.1 MIBs, e.g. not pysmi pre-compiled ones, you should use .addMibCompiler or .addAsn1MibSource for setting up search path.
Despite its name, .addMibCompiler/.addAsn1MibSource do not add a path but set a new one(s) for given MibBuilder instance. Thus you should always specify all sources of MIBs your application might need for MIBs you refer to and for MIBs imported by those you refer to (and that goes recursively).
You can pass the destination keyword parameter to .addMibCompiler/.addAsn1MibSource functions to alter compiled MIBs location.
Having said that I'd propose to try:
addMibCompiler(mibBuilder, sources=['/home/krish/mibs', '/usr/share/snmp/mibs'])
or
ObjectType(ObjectIdentity('VLAN-MIB','InterfaceMode',3).addAsn1MibSource('/home/krish/mibs', '/usr/share/snmp/mibs')))
Alternatively, if you want to stick to just /home/krish/mibs, try copying all required MIBs into that directory. Import errors from pysnmp report missing dependencies.
Finally, there is a large collection of various MIBs on-line you could configure pysnmp to automatically download and use:
addMibCompiler(mibBuilder, sources=['http://mibs.snmplabs.com/asn1/#mib#'], destination='/home/krish/mibs')