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Table Of Contents
Restrictions for the IP SLAs Random Scheduler
Information About the IP SLAs Random Scheduler
How to Enable the IP SLAs Random Scheduler
Enabling the IP SLAs Random Scheduler
Configuration Examples for the IP SLAs Random Scheduler
Enabling the IP SLAs Random Scheduler: Example
IP SLAs Random Scheduler
The IP SLAs Random Scheduler feature is an enhancement to the existing IP SLAs Multiple Operation Scheduling feature introduced in Cisco IOS Release 12.3(8)T. The IP SLAs Multiple Operation Scheduling feature provided the capability to easily schedule multiple IP SLAs operations to begin at intervals equally distributed over a specified duration of time and to restart at a specified frequency. With the IP SLAs Random Scheduler feature, you can now schedule multiple IP SLAs operations to begin at random intervals uniformly distributed over a specified duration of time and to restart at uniformly distributed random frequencies within a specified frequency range. Random scheduling improves the statistical metrics for assessing network performance.
History for the IP SLAs Random Scheduler Feature
Finding Support Information for Platforms and Cisco IOS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.
Contents
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Restrictions for the IP SLAs Random Scheduler
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Restrictions for the IP SLAs Random Scheduler
This feature is not in compliance with RFC2330, because it does not account for inter-packet randomness.
Information About the IP SLAs Random Scheduler
To enable the IP SLAs random scheduler option, you should understand the following concept:
IP SLAs Random Scheduler
The IP SLAs random scheduler option is disabled by default. To enable the random scheduler option, you must set a frequency range when configuring the ip sla monitor group schedule command in global configuration mode. The group of operations restarts at uniformly distributed random frequencies within the specified frequency range. The following guidelines apply for setting the frequency range:
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The following guidelines apply if the random scheduler option is enabled:
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How to Enable the IP SLAs Random Scheduler
This section contains the following task:
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Enabling the IP SLAs Random Scheduler
Perform this task to schedule multiple IP SLAs operations to begin at random intervals uniformly distributed over a specified duration of time and to restart at uniformly distributed random frequencies within a specified frequency range.
Prerequisites
Before scheduling a group of operations, you should configure all the IP SLAs operations that will be used in that group. For information on configuring IP SLAs operations, see the "Related Documents" section.
SUMMARY STEPS
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DETAILED STEPS
Configuration Examples for the IP SLAs Random Scheduler
This section contains the following configuration example:
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Enabling the IP SLAs Random Scheduler: Example
The following example shows how to schedule IP SLAs operations 1 to 3 as a group (identified as group 2). In this example, the operations are scheduled to begin at uniformly distributed random intervals over a schedule period of 50 seconds. The first operation is scheduled to start immediately. The random scheduler option is enabled and the uniformly distributed random frequencies at which the group of operations will restart is chosen within the range of 80-100 seconds.
ip sla monitor group schedule 2 1-3 schedule-period 50 frequency range 80-100 start-time nowAdditional References
The following sections provide references related to the IP SLAs Random Scheduler feature.
Related Documents
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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MIBs
CISCO-RTTMON-MIB
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.
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Technical Assistance
Command Reference
This section documents one modified command only.
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ip sla monitor group schedule
To perform group scheduling for IP SLAs operations, use the ip sla monitor group schedule command in global configuration mode. To stop the operation and place it in the default state of normal scheduling, use the no form of this command.
ip sla monitor group schedule group-operation-number operation-id-numbers schedule-period seconds [ageout seconds] [frequency [seconds | range random-frequency-range]] [life {forever | seconds}] [start-time {hh:mm[:ss] [month day | day month] | pending | now | after hh:mm:ss}]
no ip sla monitor group schedule
Syntax Description
Defaults
The operation is placed in a pending state (that is, the operation is enabled but is not actively collecting information).
Command Modes
Global configuration
Command History
12.3(14)T
This command was introduced to replace the rtr group schedule command.
12.4(2)T
The range keyword and random-frequency-range argument were introduced.
Usage Guidelines
Though IP SLAs multiple operations scheduling functionality helps in scheduling thousands of operations, you should be cautious while specifying the number of operations, the schedule period, and the operation group frequency to avoid any significant CPU impact.
For example, consider a scenario where you are scheduling 1 to 780 operations at a schedule period of 60 seconds. The command would be as follows:
ip sla monitor group schedule 2 1-780 schedule-period 60 start-time now
IP SLAs calculates how many operations it should start in each 1-second interval by dividing the number of operations by the schedule period (780 operations divided by 60 seconds, which is 13 operations per second). Operations 1 to 13 in operation group 2 start after 0 seconds, operations 14 to 26 start after 1 second, operations 27 to 40 start after 2 seconds, and the iteration continues until operations 768 to 780 start after 59 seconds. This high value of operations starting at every 1-second interval (especially for jitter operations) can load the CPU to very high values.
On a Cisco 2600 router, the maximum recommended value of operations per second is 6 or 7 (approximately 350 to 400 operations per minute). Exceeding this value of 6 or 7 operations per second could cause major performance (CPU) impact. Note that the maximum recommended value of operations per second varies from platform to platform.
Note
When you reboot the router, the IP SLAs multiple operations scheduling functionality schedules the operations in the same order as was done before the reboot. For example, assume the following operation had been scheduled:
ip sla monitor group schedule 2 1-20 schedule-period 40 start-time now
Over a range of 40 seconds, 20 operations have to be started (that is, one operation every 2 seconds). After the system reboot, operation 1 will start at t seconds and operation 2 starts at t+2 seconds, operation 3 starts at t+4 seconds, and so on.
The IP SLAs multiple operations scheduling functionality schedules the maximum number of operations possible without aborting. However, this functionality skips those IP SLAs operations that are already running or those that are not configured and hence do not exist. The total number of operations will be calculated based on the number of operations specified in the command, irrespective of the number of operations that are missing or already running. The IP SLAs multiple operations scheduling functionality displays a message showing the number of active and missing operations. However, these messages are displayed only if you schedule operations that are not configured or are already running.
IP SLAs Random Scheduler
The IP SLAs random scheduler option provides the capability to schedule multiple IP SLAs operations to begin at random intervals over a specified duration of time. The random scheduler option is disabled by default. To enable the random scheduler option, you must configure the frequency range random-frequency-range keywords and argument. The group of operations restarts at uniformly distributed random frequencies within the specified frequency range. The following guidelines apply for setting the frequency range:
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The following guidelines apply if the random scheduler option is enabled:
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Examples
The following example shows how to schedule IP SLAs operations 3, 4, and 6 to 10 as a group (identified as group 1). In this example, the operations are scheduled to begin at equal intervals over a schedule period of 20 seconds. The first operation (or set of operations) is scheduled to start immediately. Since the frequency is not specified, it is set to the value of the schedule period (20 seconds) by default.
ip sla monitor group schedule 1 3, 4, 6-10 schedule-period 20 start-time nowThe following example shows how to schedule IP SLAs operations 1 to 3 as a group (identified as group 2). In this example, the operations are scheduled to begin at random intervals over a schedule period of 50 seconds. The first operation is scheduled to start immediately. The random scheduler option is enabled and the frequency at which the group of operations will restart will be chosen randomly within the range of 80-100 seconds.
ip sla monitor group schedule 2 1-3 schedule-period 50 frequency range 80-100 start-time nowRelated Commands
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