If you have to maintain hundreds or thousands of IP SLAs to keep track of various network performance metrics, scheduling your IP SLA probes with a group schedule will save you time and effort when compared to scheduling an IP SLA probe one at a time. Additionally, router and switch processors have a limit that varies from platform to platform, of how many IP SLA probes can be scheduled at a given time. When this limit is reached or exceeded it can severely impact the performance and basic operation of services and features employed on a device. An IP SLA group schedule is a single line of syntax that can help space out the execution of IP SLA probes, aiding in future scalability and reducing administrative overhead.
An individual IP SLA probe, in IOS 12.4 T, is created with the following syntax:
(config)#ip sla 1 (config)#ip sla [number]
We’ll be using the most basic of IP SLA probes for this example, the icmp-echo. The icmp-echo sub-command is used to issue an ICMP echo request from a specific source to a specific destination.
(config-ip-sla)#icmp-echo 1.1.1.1 source-ip 2.2.2.2 (config-ip-sla)#icmp-echo [destination IP address] source-ip [IP address] (config-ip-sla)#icmp-echo [destination IP address] source-interface [interface]
Note: An IP SLA probe cannot be modified after leaving its config-ip-sla mode, and must be removed and re-added, if a change needs to be made.
The IP SLA probes are tied together with an IP SLA group schedule. An IP SLA group schedule can be used to space out traffic generated by IP SLA monitors.
The group schedule defines which IP SLA monitors you want to include, how often you want individual IP SLA monitors spaced out, how often the group schedule is active and the start and lifetime of the group schedule.
(config)#ip sla group schedule 1 1-10 schedule-period 60 frequency 300 start-time now life forever (config)#ip sla group schedule [schedule-id] [IP SLA monitor(s)] (you can use dashes and commas for discontinuous numbers) schedule-period [period of time in seconds that is divided by the number of IP SLA monitors] frequency [time-interval in seconds] start-time [IP SLA group first run-time] life [duration IP SLA group operates]
A group schedule can be modified on the fly to include additional, or exclude existing IP SLA probes. We can also reschedule a group which basically restarts or refreshes the group from the moment the reschedule command is issued.
(config)#ip sla group schedule 1 ? WORD Multiple probe ID's to be group scheduled add Add probes to existing group delete delete probes from existing group reschedule Reschedule the group using previous config
We can verify the IP SLA group schedule status with the “show ip sla group schedule [#]” command:
#show ip sla group schedule 1 Group Entry Number: 1 Probes to be scheduled: 1-10 Total number of probes: 10 Schedule period: 60 Mode: even Group operation frequency: 300 Status of entry (SNMP RowStatus): Active Next Scheduled Start Time: Start Time already passed Life (seconds): Forever Entry Ageout (seconds): never
In this example there are 10 IP SLA probes with a schedule period of 60 seconds, a frequency of 300 seconds, a start time of now and a lifetime of forever. Therefore, an ICMP echo request will be sent out every 6 seconds, for 60 seconds, in 300 second intervals, from the moment the group schedule command is entered, for as long as the router/switch lives for.
ip sla group schedule 1 1-10 schedule-period 60 frequency 300 start-time now life forever
We can verify the scheduling behavior by issuing the command “show ip sla statistics | include” and including the string “Latest operation s” (case sensitive). The following output shows an IP SLA probe being kicked off every six seconds.
#show ip sla statistics | include Latest operation s Latest operation start time: *02:32:51.731 UTC Fri Mar 5 2013 Latest operation start time: *02:32:57.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:03.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:09.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:15.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:21.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:27.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:33.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:39.723 UTC Fri Mar 5 2013 Latest operation start time: *02:33:45.723 UTC Fri Mar 5 2013
If the schedule period is set to be greater than the frequency, the IP SLA probes will overlap every frequency interval, in which case IP SLA probes will be scheduled simultaneously.
The following group schedule uses 10 IP SLA probes with a schedule period of 120 seconds, a frequency of 60 seconds, a start time of now and a lifetime of forever. Therefore, a probe will be scheduled every 12 seconds, for 120 seconds, in 60 second intervals. By the second frequency interval, two IP SLA probes will be kicked off together, every 12 seconds.
ip sla group schedule 1 1-10 schedule-period 120 frequency 60 start-time now life forever
We can verify this behavior by issuing the “show ip sla statistics | i Latest operation s” command. The output below shows two IP SLA probes being kicked off every 12 seconds.
#show ip sla statistics | i start Latest operation start time: *00:20:52.403 UTC Fri Mar 5 2013 Latest operation start time: *00:21:04.395 UTC Fri Mar 5 2013 Latest operation start time: *00:21:16.395 UTC Fri Mar 5 2013 Latest operation start time: *00:21:28.395 UTC Fri Mar 5 2013 Latest operation start time: *00:21:40.395 UTC Fri Mar 5 2013 Latest operation start time: *00:20:52.395 UTC Fri Mar 5 2013 Latest operation start time: *00:21:04.395 UTC Fri Mar 5 2013 Latest operation start time: *00:21:16.395 UTC Fri Mar 5 2013 Latest operation start time: *00:21:28.395 UTC Fri Mar 5 2013 Latest operation start time: *00:21:40.395 UTC Fri Mar 5 2013
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Below is a basic configuration example for ten destinations using the first group schedule that was demonstrated.
ip sla 1 icmp-echo 1.1.1.1 source-ip 2.2.2.2 ! ip sla 2 icmp-echo 1.1.1.2 source-ip 2.2.2.2 ! ip sla 3 icmp-echo 1.1.1.3 source-ip 2.2.2.2 ! ip sla 4 icmp-echo 1.1.1.4 source-ip 2.2.2.2 ! ip sla 5 icmp-echo 1.1.1.5 source-ip 2.2.2.2 ! ip sla 6 icmp-echo 1.1.1.6 source-ip 2.2.2.2 ! ip sla 7 icmp-echo 1.1.1.7 source-ip 2.2.2.2 ! ip sla 8 icmp-echo 1.1.1.8 source-ip 2.2.2.2 ! ip sla 9 icmp-echo 1.1.1.9 source-ip 2.2.2.2 ! ip sla 10 icmp-echo 1.1.1.10 source-ip 2.2.2.2 ! ip sla group schedule 1 1-10 schedule-period 60 frequency 300 start-time now life forever
