Re: Help understanding "OID not increasing"

On Thu, 2018-08-02 at 08:30 -0700, Bill Fenner wrote:
> On Tue, Jul 24, 2018 at 4:20 AM Mark Gillott 
> mail.com> wrote:
> > I have a generated a small enterprise MIB to represent some QoS
> > objects
> > (traffic classes, queue lengths, drops, tail drops, etc) for
> > particular
> > system. The whole thing is driven by a Perl pass-persist extension
> > script (using SNMP::Extension::PassPersist). With one exception it
> > all
> > works fine - objects get populated and the tables can be walked.
> > 
> > The exception is a table that is optional. That is a table
> > consisting
> > of a name and a counter that may not exist - all depends on the
> > underling configuration. Provided the object ("DSCP WRED Map")
> > exists
> > all is fine:
> > 
> > VM-1:$ snmpwalk -v2c -c public localhost ATT-VROUTER-QOS-
> > MIB::qosDSCPWREDMapTable
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapEntry.1.7.0.0.0.1 = INTEGER: 1
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapEntry.1.7.1.0.0.1 = INTEGER: 1
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapEntry.1.10.0.0.0.1 = INTEGER: 1
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapEntry.1.10.1.0.0.1 = INTEGER: 1
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapName.7.0.0.0.1 = STRING: test
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapName.7.1.0.0.1 = STRING: test
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapName.10.0.0.0.1 = STRING: test
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapName.10.1.0.0.1 = STRING: test
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapDropPkts.7.0.0.0.1 = Counter64:
> > 0
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapDropPkts.7.1.0.0.1 = Counter64:
> > 0
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapDropPkts.10.0.0.0.1 = Counter64:
> > 0
> > ATT-VROUTER-QOS-MIB::qosDSCPWREDMapDropPkts.10.1.0.0.1 = Counter64:
> > 0
> > VM-1:$ 
> > 
> > But if the underlying object has not been defined, I get:
> > 
> > VM-1:$ snmpwalk -v2c -c public localhost ATT-VROUTER-QOS-
> > MIB::qosDSCPWREDMapTable
> > ATT-VROUTER-QOS-MIB::qosShaperClass.7.0 = INTEGER: 7
> > Error: OID not increasing: ATT-VROUTER-QOS-MIB::qosDSCPWREDMapTable
> >  >= ATT-VROUTER-QOS-MIB::qosShaperClass.7.0
> > 
> > VM-1:$ snmpwalk -On -v2c -c public localhost ATT-VROUTER-QOS-
> > MIB::qosDSCPWREDMapTable
> > .1.3.6.1.4.1.74.1.32.1.1.1.1.1.7.0 = INTEGER: 7
> > Error: OID not increasing: .1.3.6.1.4.1.74.1.32.1.5.1
> >  >= .1.3.6.1.4.1.74.1.32.1.1.1.1.1.7.0
> > 
> > VM-1:$ 
> > 
> > The OID ".1.3.6.1.4.1.74.1.32.1.1.1.1.1.7.0" is the very first
> > element
> > of the MIB, i.e. the PassPersist module is walking the objects and
> > this
> > is the very first element. But why the complaint?
> The complaint is because the manager asked for the next object
> after  .1.3.6.1.4.1.74.1.32.1.5.1, and the agent
> returned .1.3.6.1.4.1.74.1.32.1.1.1.1.1.7.0, which is not after, it's
> before.  If snmpwalk did not complain and stop, it would never
> terminate.  Try "snmpwalk -Cc" to see this loop.
> 
> > Is there anything I can do to get PassPersist to return "no such
> > object"?
> If the table is the last item in your MIB module,  try returning
> "NONE".  Otherwise, return the next object after the table.
> 
Thanks for the reply. 
The trouble is, the core handler and OID database is maintained by
PassPersist. I cannot see a way for my controlling script to intercept
a request for .1.3.6.1.4.1.74.1.32.1.5.1, check for the existence of
the underlying object and return NONE (or the next object).
I guess I have to dig further into PassPersist module, see if there are
any hooks. Failing that it looks like I'd have to ditch PassPersist
library module and do everything myself - which is not going to be fun.
Mark
>   Bill
> 
> > 
> > Thanks,
> > 
> > Mark
> > 
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