# SNMP data constraints verification error

17. Will PySNMP Manager verify the values it sends to and receives from a distant Agent against local MIB constraints?

1. Yes, it can do that. The Manager will verify the values you pass to SET request against a MIB if:

   The values are not already PyASN1 objects but some basic Python types (like integer or string). You tell PySNMP engine to load appropriate MIB where it could lookup the constraints (via the use of MibVariable) So, the following code fragment makes PySNMP engine loading SNMPv2-MIB and verifying that the ‘new system name’ value satisfies sysName constraints (if any).

    errorIndication, errorStatus, errorIndex, varBinds = cmdGen.setCmd(
        cmdgen.CommunityData('public'),
        cmdgen.UdpTransportTarget(('localhost', 161)),
        ( cmdgen.MibVariable('SNMPv2-MIB', 'sysName', 0), 'new system name' )
    )

To verify the response values, you should pass at least lookupValues flag to CommandGenerator *cmd() method you use. In the following example PySNMP will make sure that Agent-supplied value for SNMPv2-MIB::sysName Managed Object satisfies MIB constraints (if any).

    errorIndication, errorStatus, errorIndex, varBinds = cmdGen.getCmd(
        cmdgen.CommunityData('public'),
        cmdgen.UdpTransportTarget(('localhost', 161)),
        cmdgen.MibVariable('SNMPv2-MIB', 'sysName', 0),
        lookupValues=True
    )

In case of constraint violation, a PySNMP exception will be raised.