I have played a bit more and the conjecture turned out to be (at least
partially) false.
The way I played was attempt to query string objects with long values:
$ snmpget -v 2c -c public 192.168.1.1 IF-MIB::ifAlias.3
IF-MIB::ifAlias.3 = STRING: Builtin r8139/8129 - Realtek RTL8139 Fast
Ethernet Bus 0 Slot
$ { for i in {1..13}; do echo 'IF-MIB::ifAlias.3'; done } | xargs
snmpget -d -r 0 -v 2c -c public 192.168.1.1
Sending 254 bytes to UDP: [192.168.1.1]:161->[0.0.0.0]:0
...
Timeout: No Response from 192.168.1.1.
So the device sends no response to a 254-byte request. If 12 copies are
queried, then it works OK by responding with a 1020-byte packet.
Aleksandrs
On 11/19/2013 10:59 AM, Aleksandrs Saveljevs wrote:
> I have played with your suggestion by querying a different set of OIDs
> and I am starting to think it might a limit not on the response size or
> the number of OIDs, but on the size of the inbound UDP packet.
>
> So sometimes our device returned a response to 28 OIDs and failed on 29
> OIDs, and sometimes it returned a response to 29 OIDs and failed on 30.
>
> However, it was consistently returning responses when snmpget was
> sending packets up to 484 bytes and not returning responses to requests
> at least 485 bytes in size.
>
> Aleksandrs
>
> On 11/16/2013 12:09 AM, "Fredrik Björk" wrote:
>> Hi!
>>
>> What if you replace "head -29 walk.txt" with "head -100 walk.txt | tail
>> -29" to get another set of OIDs? Still 29 OK not 30? In that case, it's
>> definitely D-link just supporting 29 OIDs just because they didn't feel
>> more was required.
>>
>> /Fredrik
>>
>> PS dd-wrt on a WRT-54GL returns 128 variables upon request - that's REAL
>> software! /DS
>>
>>> Good morning,
>>>
>>> We have some SNMP devices that do not respond to queries where the
>>> number of OIDs is over a certain limit. That is, they do respond to
>>> queries with N OIDs in the request, but return no response to queries
>>> with N+1 and more OIDs.
>> ...
>>> $ head -29 walk.txt | cut -d' ' -f1 | xargs snmpget -d -r 0 -v 2c -c
>>> public 192.168.1.1
>>
>>
>>
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