[Xymon] Devmon tests clear but snmpwalk works

Fri May 27 01:49:25 CEST 2016

On Fri, 27 May 2016, 08:46 Colin Coe <colin.coe at gmail.com> wrote:

> Hi all and many thanks for all the replies.
>
> Jeremy: I did the tcpdump as per the thread and found that the R= value
> was significantly less than the maximum 32 bit integer on some of the
> switches but negative on others.  Censored, truncated output follows.  How
> do we deal with the negative numbers?
>

Can you confirm if positive IDs are accepted by devmon? If not, this might
be a red herring.

OK, so I'm no SNMP expert, but this is what I think is happening.  When a
large 64bit integer (greater than 2^32-1) that is cast to a 32bit integer,
the highest bit is interpreted as a sign bit of 1, meaning negative. The
request ID can be a 64bit integer, but not greater than 2^32-1.  But some
switches convert into an incompatible type that causes problems with 32bit
libraries.  Some builds of SNMP libraries have an API option to avoid
sending requests with negative IDs.

In my case, I think I had a 32bit MRTG package installed on a 64bit OS, and
I had to uninstall it and reinstall the 64bit version of package. I'm
guessing that the 32bit version sent out negative IDs in queries but
couldn't cope with the 64bit values in the responses. It's also possible
that I remember things wrongly (it was a loooong time ago), so don't trust
my conjecture about the cause but of this.

I recall some people recompiled their Perl module to enable the "avoid
using negative IDs" option in the API.

More here:

https://lists.oetiker.ch/pipermail/mrtg-developers/2002-September/000103.html

This link mentions Dell switches but my problem was with Cisco switches.

J

---
> 06:35:54.584298 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP
> (17), length 72)
>     172.22.106.11.60150 > 192.168.78.254.snmp:  { SNMPv2c C=public {
> GetRequest(28) R=-2032073048  .1.3.6.1.2.1.1.1.0 } }
> 06:35:55.153728 IP (tos 0x0, ttl 254, id 47570, offset 0, flags [none],
> proto UDP (17), length 335)
>     192.168.78.254.snmp > 172.22.106.11.60150:  { SNMPv2c C=public {
> GetResponse(287) R=-2032073048  .1.3.6.1.2.1.1.1.0="Cisco IOS Software,
> CGS2520 Software (CGS2520-IPSERVICESK9-M), Version censored, RELEASE
> SOFTWARE (fc1)^M^JTechnical Support: http://www.cisco.com/techsupport^M^JCopyright
> (c) 1986-2011 by Cisco Systems, Inc.^M^JCompiled sometime by prod_rel_team"
> } }
> 06:35:55.157010 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP
> (17), length 78)
>     172.22.106.11.60150 > 192.168.78.254.snmp:  { SNMPv2c C=public {
> GetRequest(34) R=-2032073047  .1.3.6.1.4.1.9.9.109.1.1.1.1.5.1 } }
> 06:35:55.731062 IP (tos 0x0, ttl 254, id 47571, offset 0, flags [none],
> proto UDP (17), length 79)
>     192.168.78.254.snmp > 172.22.106.11.60150:  { SNMPv2c C=public {
> GetResponse(35) R=-2032073047  .1.3.6.1.4.1.9.9.109.1.1.1.1.5.1=5 } }
> 06:35:55.732084 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP
> (17), length 74)
>     172.22.106.11.60150 > 192.168.78.254.snmp:  { SNMPv2c C=public {
> GetRequest(30) R=-2032073046  .1.3.6.1.4.1.9.2.1.2.0 } }
> 06:35:56.316063 IP (tos 0x0, ttl 254, id 47572, offset 0, flags [none],
> proto UDP (17), length 82)
>     192.168.78.254.snmp > 172.22.106.11.60150:  { SNMPv2c C=public {
> GetResponse(38) R=-2032073046  .1.3.6.1.4.1.9.2.1.2.0="power-on" } }
> ---
>
> Nikolai: I'm a bit hesitant to apply patches like this so I'll exhaust all
> other avenues before looking at this.
>
> Paul: Double checked Devmon's hosts.db and I can confirm the details are
> correct.
>
> Thanks
>
>
> On Thu, May 26, 2016 at 9:38 PM, Root, Paul T <Paul.Root at centurylink.com>
> wrote:
>
>> Look in your hosts.db file, and see if the switches are identified as the
>> proper template and that the community string is correct. The newer NX type
>> switches do not work with the old template.
>>
>>
>>
>> Use snmpwalk/snmpget to pull some of the OIDs of the template.
>>
>>
>>
>> *From:* Xymon [mailto:xymon-bounces at xymon.com] *On Behalf Of *Colin Coe
>> *Sent:* Thursday, May 26, 2016 7:21 AM
>> *To:* xymon at xymon.com
>> *Subject:* [Xymon] Devmon tests clear but snmpwalk works
>>
>>
>>
>> Hi all
>>
>>
>>
>> I know this is the Xymon list not Devmon but I think I'll have most luck
>> on this list so apologies in advance.
>>
>>
>>
>> I have a few of Cisco switches that I've just started monitoring at a
>> couple of remote sites. snmpwalk works from the Xymon server but the Devmon
>> tests are all clear (Devmon runs on the Xymon server).
>>
>>
>>
>> When I look at the devmon.log I just see lots of
>>
>> ---
>>
>> [16-05-26 at 20:19:09] No SNMP data found for ifName on swi02
>>
>> [16-05-26 at 20:19:09] No SNMP data found for ifOutPktsSec on swi02
>>
>> [16-05-26 at 20:19:09] No SNMP data found for ifOutCollisions on swi02
>>
>> ---
>>
>>
>>
>> Any ideas on tracking this down?
>>
>>
>>
>> We have many if these switches at other sites and they display correctly
>> in Xymon.
>>
>>
>>
>> Thanks
>>
>>
>>
>> CC
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>
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