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manual:087:4_help.2_debugging [2010/12/01 15:10]
gandalf be precise on script timeout
manual:087:4_help.2_debugging [2012/11/30 10:14] (current)
gandalf tackling snmpbulkwalks
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 All output is printed to STDOUT in both cases. This procdure allows for repeated tests without waiting for the next polling interval. And there's no need to manually search for the failing host between hundreds of lines of output. All output is printed to STDOUT in both cases. This procdure allows for repeated tests without waiting for the next polling interval. And there's no need to manually search for the failing host between hundreds of lines of output.
  
 +==== Check Bulkwalk Behaviour (SNMP Data Queries only) ====
 +
 +The goal of bulkwalks is to reduce SNMP traffic overhead. It works by cramming several SNMP requests/responses into a single IP packet. This feature is not available with SNMP version 1. Some SNMP enabled devices do not like snmpbulkwalks. 
 +
 +Cacti supports this feature with SNMP enabled devices automatically when version 2 or version 3 has been selected. The field "max OIDs" for each hosts governs, how many packets are crammed together. Side note: In case too many SNMP packets will be crammed together, IP fragmentation takes care of splitting those into chunks manageable by the IP layer.
 +You will see such an effect when e.g. your manual 
 +<code>snmpwalk -c <community string> -v 2c <target> <OID></code>
 +produces a result but cacti poller output shows NaN.
 +
 +Now you have two different means to tackle such an issue:
 +  - reduce "max OIDs" to 1: Cacti now will disable all Cacti-internal mechanisms to use snmpbulkwalk
 +  - select SNMP version 1: as SNMP V1 does not support snmpbulkwalks, all Cacti-internal and Cacti-external bulkwalk mechanisms are disabled
 +
 +Discussion:\\ 
 +**Cacti-internal bulkwalk mechanisms**: Spine checks the "max OIDs". In case they are set to a value higher than 1, we will use snmpbulkwalk-like code. Else, we use standard snmpwalks.\\ 
 +
 +**Cacti-external bulkwalk mechanisms**: It has been found, that php-snmp automatically uses snmpbulkwalk, even when only snmpwalk has been requested. As of current, php-snmp will join 20 requests/response. We can't change this setting externally. So the ultimate answer to this is to use SNMP version 1. The drawback of using SNMP version 1 is that e.g. COUNTER64 is **not** available with this setting. As a result, e.g. a **Verbose Query** from within the browser may fail while spine still works. Yes, crazy.
 ==== Check MySQL Update ==== ==== Check MySQL Update ====
  





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