Poll Sensitive and Critical Devices Without a Performance Impact

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Poll Sensitive and Critical Devices Without a Performance Impact

As the Administrator, you know which of your critical devices are sensitive to too many polls, which can lead to performance problems. However, to ensure the performance of your critical devices, you must somehow monitor these sensitive devices. By configuring the SNMP polling controls, you can throttle the SNMP poll requests and avoid overwhelming your sensitive devices.

By default, SNMP polling is controlled in two ways:

SNMP traffic threshold — No more than 15 SNMP requests can be sent to a device at a time. Poll and discovery SNMP requests over 15 are queued and sent to a device when possible during the polling cycle. Up to 600 requests can be queued.
SNMP timeouts threshold — When 15 or more SNMP requests timeout, polling is suspended for the remainder of the current polling cycle. An event is generated, informing you of the situation.
Note: Polling resumes at the beginning of each poll cycle. When the timeouts do not exceed the 15 threshold, a "clear" event is generated.

Both thresholds are designed to prevent overwhelming a device with poll requests. However, you can configure these SNMP polling thresholds, when needed.

For example, your older router is exceptionally sensitive to polling. But, this router is critical and must be polled as frequently as possible. You already adjusted your monitoring profile to remove unnecessary metric families from polling. You also applied a filter in your monitoring profile to reduce the number of polled interfaces. However, polling still causes this router to crash. Therefore, your only option is to adjust the default SNMP polling parameters for your sensitive router.

Certain parameters, such as the following, may be added to the policy for individual IPs or IP ranges in an IPRange section within the IPRangeList:

MaxOutstandingRequests

The maximum number of outstanding requests sent to the devices within the indicated IP range.

MaxRequestSize

Limits the number of OIDs in an outgoing SNMP request. If the number of OIDs in the SNMP request exceeds the value of MaxRequestSize, the outgoing request is split into two or more smaller requests.

Some IP ranges are not covered in the IPRange sections. For global settings, use the MaxRequestSizeDefault parameter to set the OID limit.

Follow these steps:

Find the ID for your IP Domain (that contains your sensitive router) by opening:
```
http://hostname:port/rest/ipdomains
```
hostname:port

Specifies the Data Aggregator hostname and the port number where you are accessing the REST web services from.
Locate your IP Domain ID in the following SNMP throttle policy list, and note the corresponding policy ID:
```
http://hostname:port/rest/snmpthrottlepolicies
```
Determine the number of OIDs that you want to include in a single outgoing SNMP request. Some devices ignore requests that are too large without sending an error. As a result, the SNMP poller cannot reach the device. Use the MaxRequestSize value to allow the Data Collector to monitor these devices.
Example

If the interface SNMP request has 27 OIDs and MaxRequestSizeDefault is set to 15, the outgoing request is split into two smaller requests. One request contains 14 OIDs, and the other contains 13 OIDs.

Example: The following example from an SNMP throttle policy shows that the policy ID is "601" for IP Domain "2" with no limit on the number of OIDs:
```
<SnmpThrottlePolicy version="1.0.0">
```
```
<ID>601</ID> 
<MaxOutstandingRequestsDefault>15</MaxOutstandingRequestsDefault> 
<QueueLength>600</QueueLength> 
<TimeoutFailSafeThrottleDefault>15</TimeoutFailSafeThrottleDefault>
<MaxRequestSizeDefault>0</MaxRequestSizeDefault> 
 <IPDomainID>2</IPDomainID> 
</SnmpThrottlePolicy>
```
Open a REST client editor or HTTP tool that sends requests and gets responses, and set the Content-type to application/xml.
Open and edit the SNMP throttle policy for your IP Domain by entering the following criteria:
- URL: http://hostname:port/rest/snmpthrottlepolicies/policyID
  
  policyID
  
  Specifies a unique identification number that is assigned to the SNMP throttle policy for the IP Domain that contains your sensitive device.
  
  Example: http://hostname:port/rest/snmpthrottlepolicies/601
- HTTP method = PUT
- Adjust the following values for your IP Range on the Body tab in the HTTP Request pane:
  - <MaxOutstandingRequests> – SNMP traffic threshold
  - <TimeoutFailSafeThrottle> – SNMP timeouts threshold
  Note: Both values are required for every IP Range entry. You can disable either parameter by setting the value to "0."
- Remove the following lines:
  - <ID>
  - <IPDomainID>
Results are returned in the Body tab of the HTTP Response pane.

Example: In this example, the thresholds are lowered to "10" for device 10.231.41.7 only. For this device, the number of OIDs is limited to 50. The default thresholds and other IP Range thresholds continue using the default value of "15." For devices 10.231.41.1-10.231.41.255, SNMP requests are limited to 30 OIDs.
```
<SnmpThrottlePolicy version="1.0.0">
```
```
<IPRangeList>
  <IPRange>
        <IPRangeText>10.231.41.7</IPRangeText>
        <MaxOutstandingRequests>10</MaxOutstandingRequests>
        <TimeoutFailSafeThrottle>10</TimeoutFailSafeThrottle>
		<MaxRequestSize>50</MaxRequestSize>
  </IPRange>
  <IPRange>
        <IPRangeText>10.231.41.1-10.231.41.255</IPRangeText>
        <MaxOutstandingRequests>15</MaxOutstandingRequests>
        <TimeoutFailSafeThrottle>15</TimeoutFailSafeThrottle>
		<MaxRequestSize>30</MaxRequestSize>
  </IPRange>
</IPRangeList>
    <MaxOutstandingRequestsDefault>15</MaxOutstandingRequestsDefault>
    <QueueLength>600</QueueLength>
    <TimeoutFailSafeThrottleDefault>15</TimeoutFailSafeThrottleDefault>
```
```
</SnmpThrottlePolicy>
```
Note: You can adjust the thresholds for a single device or a range of devices. The IP Range definition and the IP Range order determine which threshold applies. The IP Ranges are listed in priority order. That is, the first IP Range that applies to a device determines the threshold value to apply.

Always include the MaxOutstandingRequestsDefault, TimeoutFailSafeThrottleDefault, and QueueLength parameters in the update/POST XML at the root level. Include the parameters even if the values do not differ from the default.

Example:

This PUT command generates the policy that follows.

 Update XML: PUT on URL DA-HOST:8581/rest/snmpthrottlepolicies/21

<SnmpThrottlePolicy version="1.0.0">
<IPRangeList>

  <IPRange>

    <IPRangeText>130.119.103.8</IPRangeText>
    <MaxOutstandingRequests>10</MaxOutstandingRequests>
    <TimeoutFailSafeThrottle>10</TimeoutFailSafeThrottle>
       <MaxRequestSize>20</MaxRequestSize>
  </IPRange>
</IPRangeList>
<MaxRequestSizeDefault>50</MaxRequestSizeDefault>
<MaxOutstandingRequestsDefault>15</MaxOutstandingRequestsDefault>
<TimeoutFailSafeThrottleDefault>15</TimeoutFailSafeThrottleDefault>
<QueueLength>600</QueueLength>
</SnmpThrottlePolicy>

This command generates the following policy:

<SnmpThrottlePolicy version="1.0.0">
<ID>21</ID>
<QueueLength>600</QueueLength>
<TimeoutFailSafeThrottleDefault>15</TimeoutFailSafeThrottleDefault>
<IPDomainID>2</IPDomainID>
<IPRangeList>
<IPRange>
<IPRangeText>130.119.103.8</IPRangeText>
<MaxOutstandingRequests>10</MaxOutstandingRequests>
<TimeoutFailSafeThrottle>10</TimeoutFailSafeThrottle>
<MaxRequestSize>20</MaxRequestSize>
</IPRange>
</IPRangeList>
<MaxRequestSize>50</MaxRequestSize>
<MaxOutstandingRequestsDefault>15</MaxOutstandingRequestsDefault>
</SnmpThrottlePolicy>