[AGENT++] Problem using net-snmp as subagent (Error in packet)

[Frank Fock]

Hello Johnny,

a 0.0 OID should be encoded like:
02 00 00 00
00 00 00 00
00 00 00 00

and not
00 00 00 00

which is actually a zero length OID which
must not be returned by a SNMP agent.
Consequently, it should not be allowed for
an AgentX subagent to return a zero length
OID. Nevertheless, the AgentX++ master agent
should be able to handle this. At the moment,
I think there is no workaround implemented
to map a zero length OID to 0.0 for NET-SNMP
subagents. Instead a AgentX protocol error
is thrown, which could lead to a subagent
disconnect (if not sure if it actually does).

Hope this helps.

Best regards,
Frank

Johnny Ljunggren wrote:
> 
> Hello
> 
> Thanks for the effort so far.
> 
> I've been having a discussion with Dave Shield of net-snmp and it seems
> that the problem might be in agentpp after all. At least it looks like the
> zeroDotZero packet are built correctly on the net-snmp side (RFC 2741,
> section 5.1) but is not acknowledge on the agentpp AgentX side.
> 
> This would be the correct response to IF-MIB::ifSpecific.1 according to Dave:
> 
> Sending 64 bytes to Local IPC: /var/agentx/master
> 0000: 01 12 00 00  01 00 00 00  00 00 00 00  00 00 00 00    ................
> 0016: 2C 00 00 00  00 00 00 00  00 00 00 00  06 00 00 00    ,...............
> 0032: 06 02 00 00  01 00 00 00  02 00 00 00  02 00 00 00    ................
> 0048: 01 00 00 00  16 00 00 00  01 00 00 00  00 00 00 00    ................
> 
> looks correct for returning a response of
> 
>    .1.3.6.1.2.1.2.2.1.22.1 (ifSpecific.1) = OID .0.0
> 
> Could you have a look and give me your thoughts on this?
> 
>> Are you sure that ifSpecific.1 causes the error?
>> If you are using GETNEXT/GETBULK also the
>> ifSpecific.x following objects could cause the
>> error (this is my experience). Therefore I suggested
>> to compile only those MIBs into the NET-SNMP
>> agent that are absolutely needed.
>>
>> Hope this helps.
>>
>> Best regards,
>> Frank
>>
>> Johnny Ljunggren wrote:
>>> Hello
>>>
>>>> Sorry, my comments were mistakable. In addition to
>>>> NET_SNMP_WORKAROUNDS you will need also
>>>> to change MAX_AGENTX_REPETITIONS to 1
>>> I tried that but it didn't seem to have any effect. Maybe I did it wrong
>>> but I changed the setting to 1 then compiled the agentx library, and
>>> then
>>> recompiled my agent.
>>>
>>> I did some more research and found that only the OIDs defined as OID:
>>> SNMPv2-SMI::zeroDotZero will give this error.
>>> ie. IF-MIB::ifSpecific.1 = OID: SNMPv2-SMI::zeroDotZero
>>>
>>> I did a snmpget on every single oid and only got the problem with the
>>> above mentioned definition.
>>>
>>> I tried to look through the source code but I guess it will take me a
>>> while to get my head around what is happening.
>>>
>>> Any idea what's so special about SNMPv2-SMI::zeroDotZero and what I
>>> should
>>> be looking for?
>>>
>>>>> It seems that NET_SNMP_WORKAROUNDS is enabled by default, so I have it
>>>>> activated. Luckily I'm not running on a 64bit system, but I'm a bit
>>>>> worried anyway.
>>>>> Do you think it would be possible to pay someone with a deeper
>>>>> knowledge
>>>>> about this to fix it?
>>>>> Is net-snmp the only way to get mib-II on linux?
>>>>> Where should I start to try to solve this? (apart from contacting the
>>>>> net-snmp ml, which I already did)
>>>>>> Have you activated the NET-SNMP work-arounds in
>>>>>> agent++_def.h? The NET-SNMP AgentX implementation
>>>>>> has many bugs. For some of them, I had implemented
>>>>>> work-arounds that can be activated in AGENT++.
>>>>>>
>>>>>> I have reported those bugs to NET-SNMP.org but they
>>>>>> seem not to be able to fix them for about four years
>>>>>> now. When you run the NET-SNMP subagent on a 64bit
>>>>>> machine, things get even worse.
>>>>>>
>>>>>>> I've made a master AgentX that uses net-snmp as subagent to provide
>>>>>>> mib-II
>>>>>>> information. I get a general failure if I try to get some of the
>>>>>>> OIDs.
>>>>>>> This only occurs when running net-snmp as subagent, because it will
>>>>>>> return
>>>>>>> the whole tree if running standalone.
>>>>>>>
>>>>>>> # snmpwalk -v 2c -c public localhost
>>>>>>> <snip some output>
>>>>>>> IF-MIB::ifOutQLen.2 = Gauge32: 0
>>>>>>> IF-MIB::ifOutQLen.3 = Gauge32: 0
>>>>>>> Error in packet.
>>>>>>> Reason: (genError) A general failure occured
>>>>>>> Failed object: IF-MIB::ifOutQLen.3
>>>>>>>
>>>>>>> # snmpwalk -v 2c -c public localhost IF-MIB::ifOutQLen.3
>>>>>>> Error in packet.
>>>>>>> Reason: (genError) A general failure occured
>>>>>>> Failed object: IF-MIB::ifOutQLen.3
>>>>>>>
>>>>>>> My agent outputs this:
>>>>>>> 20070202.22:25:53: 567: (1)ERROR  : MasterAgentXMib: invalid AgentX
>>>>>>> response
>>>>>>> (sd)(sid)(tid)(req-vbs)(resp-vbs): (15), (1), (96), (1), (0)
>>>>>>>
>>>>>>> I've tried using the plain master agent from the examples directory,
>>>>>>> and
>>>>>>> net-snmp 5.3.1 and 5.4 but the results are the same.
>> --
>> AGENT++
>> http://www.agentpp.com
>> http://www.mibexplorer.com
>> http://www.mibdesigner.com
>>
>>
> 
> 

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