SNMP results unknown till check is forced

[Eirik Robertstad]

I am having a strange problem that I can't replicate on it's own.  For
the most part, but not always, it seams to happen with a Disk snmp check
to a few select windows servers.  I've also seen this happen with an
SNMP proc check, but not as bad.

The error Nagios shows is: ERROR: Description/Type table : No response
from remote host 'xxx.xxx.xxx.xxx'

For example, for the last 6 hours a Disk D: check has been coming back
as Unknown.  There are other SNMP checks on this host that come back
just fine.  We check Disks every 60 minutes, the other checks are either
60 or 30 minute checks.  There is also a Disk C: snmp check on this
host, with the same settings that has been coming back fine for almost 2
days now.

Once I do a reschedule of the check, it comes back as OK, and will
continue to do so.  Sometimes the problem will come back in a few hours,
or a few days.  The problem can jump between hosts randomly, or stick
with the same one.

I kept a tcpdump going and I can see the check happen, then come back
with an error of

"[....] udp port snmp unreachable for IP [....]"

I'm using the check_snmp_storage provided at
http://www.manubulon.com/nagios/

All checks use /usr/bin/perl and not the internal Nagios perl to execute.

To sum this up, is there any reason that this check would fail by a
normal Nagios scheduled check but not when run from the command like or
a forced reschedule in Nagios?

snipped tcpdump:

14:21:08.999137 IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF], proto
17, length: 72) nagios.35200 > DstHost.snmp: [bad udp cksum 271a!]  {
SNMPv2c C=XXXXX { GetBulk(28) R=27877  N=0 M=25 25.2.3.1.3 } }
               ........
14:21:09.015749 IP (tos 0x0, ttl 123, id 3, offset 0, flags [none],
proto 1, length: 100) DstHost > nagio
s: icmp 80: DstHost udp port snmp unreachable for IP (tos 0x0, ttl  60,
id 0, offset 0, f
lags [DF], proto 17, length: 72) nagios.35200 > DstHost.snmp: [udp sum
ok]  { SNMPv2c C=XXXXX { GetBulk(28) R=27877  N=0 M=25 25.2.3.1.3 } }
                          ....
14:21:13.998789 IP (tos 0x0, ttl  64, id 1, offset 0, flags [DF], proto
17, length: 72) nagios.35200 > DstHost.snmp: [bad udp cksum 271a!]  {
SNMPv2c C=XXXXX { GetBulk(28) R=27877  N=0 M=25 25.2.3.1.3 } }
                    ........
14:21:14.014927 IP (tos 0x0, ttl 123, id 22, offset 0, flags [none],
proto 1, length: 100) DstHost > nagi
os: icmp 80: DstHost udp port snmp unreachable for IP (tos 0x0, ttl  60,
id 1, offset 0,
flags [DF], proto 17, length: 72) nagios.35200 > DstHost.snmp: [udp sum
ok]  { SNMPv2c C=
XXXXX { GetBulk(28) R=27877  N=0 M=25 25.2.3.1.3 } }

Regards,
Eirik






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