On Fri, Mar 6, 2015 at 10:39 AM, Bill Fenner <fen...@gmail.com> wrote:
> On Thu, Mar 5, 2015 at 1:39 PM, Thomas Besemer <thomas.bese...@gmail.com>
> wrote:
>
>>
>>
>> On Thu, Mar 5, 2015 at 7:37 AM, Bill Fenner <fen...@gmail.com> wrote:
>>
>>> On Wed, Mar 4, 2015 at 11:51 AM, Thomas Besemer <
>>> thomas.bese...@gmail.com> wrote:
>>>
>>>> I am working with net-snmp 5.7.3, and will be using several Sub-Agents
>>>> in my project, with fairly large amounts of data. I have noted that
>>>> issuing a 'snmpbulkwalk' to Master Agent results in this broken down into
>>>> GETNEXT requests to the Sub-Agent. This results in a lot of network
>>>> traffic, as well as a tremendous number of context switches (everything
>>>> running on same host).
>>>>
>>>> Is there support in the Sub-Agent to accept GETBULK requests from the
>>>> Master? I have looked at the code, their appears to be some infrastructure
>>>> in place, but it is not clear to me if it is fully functional.
>>>>
>>>
>>>> More so, is there a means to configure the Master to send GETBULK
>>>> requests to the Sub-Agent?
>>>>
>>>
>>> This is something that I've been working on a little. Both of these are
>>> relatively small tweaks. However, the bigger problem is that while the
>>> subagent is processing the request, it's basically lost the scoping info
>>> that the master agent has sent it, and so the response from the subagent
>>> can include info from subtrees that the master didn't ask for. There's
>>> code in the subagent to handle this for getnext, and we could do the same
>>> for getbulk, except I was also concerned about the overhead of fetching
>>> this data within the subagent - I wanted to find a way to retain the
>>> scoping info while processing the request so that request processing could
>>> be stopped.
>>>
>>> I'd be happy to share what I have; if you're up for hacking too maybe we
>>> should create a branch on github?
>>>
>>>
>>>
>>
>> Hi Bill -
>>
>> I'd be more than happy to work with you on this, and perhaps do a github
>> branch so that when we get it working, we can generate a patch set for
>> review by community.
>>
>> My early investigation shows that Sub-Agent Doesn't handle anything but
>> GETNEXT, per handle_subagent_response() - perhaps this can be confirmed?
>> I have not looked at Master side, so it seems to me part of this could be
>> updating handle_subagent_response() to at least return some data set, if
>> this makes sense, and then have Master send OID down in PDU, and deal with
>> return data. I am assuming that a return packet from a GETBULK should be a
>> complete data set?
>>
>
> Yes, my changes include handle_subagent_response and code in the subagent
> itself.
>
>
>>
>> From what I can tell, a GETBULK PDU only contains OID, so any filtering
>> would have to be on Master side?
>>
>
> The GETNEXT and GETBULK PDUs contain SearchRangeList, which scopes the
> request. The master sends SearchRangeList for each tree that the subagent
> supports, e.g., if you have registrations of
>
> x.1 - master agent
> x.2 - subagent 1
> x.3 - subagent 2
> x.4 - subagent 1
>
> the master agent will send subagent 1 a request for x.2, scoped to [ x.2,
> x.3 ), then will ask subagent 2, then will ask subagent 1 again about [
> x.4, x.5 ). The problem with the current code in my branch is that
> subagent 1 can respond with x.2.1, x.2.2, x.4.1, x.4.2. There are two
> problems with this:
> 1) it may be expensive for the subagent to fetch x.4.1 and x.4.2 and
> they're not relevant
> 2) without filtering, the master agent will get confused by this response.
>
> We can fix 2 by filtering it, just like we already filter getnext. I
> haven't pursued this path yet because I wanted to also address 1.
>
> See https://github.com/fenner/net-snmp/tree/agentx-getbulk for my code so
> far.
>
>
> Hi Bill -
I guess I am confused here; I pulled your tree, and it only shows changes
on Master end.
Thus, a "range" sent down for an OID, which GETNEXT looks like it could
respond to by putting everything in PDU.
Please excuse my naivety, as I am relatively new to SNMP, and still sorting
out what needs to be done on PDU to Sub-Agent. RFC states that a range can
be supplied, but that range appears to be done for one OID?
My test environment is based on:
http://www.net-snmp.org/dev/agent/data__set_8c-example.html
I have added multiple rows, it responds as I expect, either giving me all
the data, or a sub-set. This all via GETNEXT (several transactions), and I
want it to come back in one packet on GETBULK. Thus, my thinking is that
PDU/Packet that comes back from Sub-Agent should have all the data I am
looking for.
If you could give me some concepts on how to fetch above example via one
GETBULK, I can do some coding, test. In general, if you give me
approaches, I will do what I can to implement, respond with patch sets for
review.
Thanks,
tom
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