How to determine maximum SNMP PDU size in a specific eHealth environment (Legacy KB ID CNC TS30151 )

Document ID : KB000051907
Last Modified Date : 14/02/2018
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eHealth supports a maximum SNMP PDU size of 8192 bytes.  Since the Mib Translation Files (MTFs) eHealth uses sometimes calls for splitting poll requests to certain devices, it is unlikely for any of eHealth's SNMP requests to reach that maximum supported size.


The maximum PDU size encountered during eHealth polling can be determined from Statistics Poller advanced logging.  If a firewall setting is involved, have the firewall admin set a temporary upper limit of PDU size to eHealth's max value of 8192 just for a few poll cycles.


Running the advanced logging during the same time this maximum value is set can help to obtain true maximum values for the current eHealth environment.  Upon determining the maximum sent and received PDU values, the firewall admin can drop the PDU size to some number a little higher than the maximum PDU size in the current eHealth environment.


1. Turn on Advanced Logging for the Statistics Poller process via the OneClick for eHealth console:


a) Select the server in the World View and log in as admin
b) Expand the tree as follows: Tasks and Information -> Setup -> Advanced Logging
c) Select the following components: Statistics Poller
d) If necessary, change the Advanced Log Directory path to a different value
e) Click Apply


2. Allow the eHealth server to poll for at least 3 poll cycles.  Verify that the $NH_HOME/log/advanced directory contains a file named nhiPoller_Net.txt after at least one poll cycle has completed.


3. Grep through nhiPoller_Net for "Pdu" to pull out the Pdu statistics as per the below example and identify the maximum values:


<servername>% grep Pdu nhiPoller_Net.txt


Pdu Response Time (sec)               NEntries 48 Total 1.82118 StdDeviation 0.0241152 Average 0.0379413 Min 0.00210595 Max 0.0984559
Xmit Pdu Bytes                        NEntries 48 Total 7959 StdDeviation 175.601 Average 165.812 Min 46 Max 996
Receive Pdu Bytes                     NEntries 21 Total 4119 StdDeviation 143.68 Average 196.143 Min 62 Max 593
Receive Pdu Bytes                     NEntries 2 Total 1492 StdDeviation 287 Average 746 Min 459 Max 1033


Pdu Response Time (sec)               NEntries 48 Total 2.02374 StdDeviation 0.0293202 Average 0.0421613 Min 0.00210714 Max 0.119452
Xmit Pdu Bytes                        NEntries 48 Total 7959 StdDeviation 175.601 Average 165.812 Min 46 Max 996
Receive Pdu Bytes                     NEntries 21 Total 4119 StdDeviation 143.68 Average 196.143 Min 62 Max 593
Receive Pdu Bytes                     NEntries 2 Total 1492 StdDeviation 287 Average 746 Min 459 Max 1033


In this example, the maximum PDU transmitted is 996 and the maximum PDU value received by eHealth is 1033.


Note that if the firewall is currently blocking some device poll responses due to PDU size, the Max in the "Receive Pdu Bytes" lines will NOT include the Max size of the blocked responses.


4. Make sure to turn off Advanced Logging for the Statistics Poller after logging a few poll cycles worth of data.

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Related Issues/Questions:
How to determine maximum SNMP PDU size in a specific eHealth environment
What is the maximum SNMP PDU used by eHealth
How to determine what maximum PDU to set for a firewall when polling with eHealth
No Response polling errors caused by a firewall filtering out SNMP requests or responses based on PDU size

Problem Environment:
eHealth
SNMP
Statistics Poller


(Legacy KB ID CNC TS30151 )