Constraints and Limitations

IP SLA uses the Tracked Object Manager‘s ICMP timing probe functionality to perform ICMP echo requests to capture timing information. The Tracked Object Manager throttles the amount of traffic it generates (128 ICMP echo requests per second, 64 UDP or TCP requests per second) to limit the amount of CPU used. Because the Tracked Object Manager is a shared resource, the throttle applies to all applications that use the Tracked Object Manager. The Tracked Object Manager further restricts statistic gathering probes to one request every tenth of a second (maximum of ten requests per seconds).

IP SLA allocates memory to support eight entries. The default functionality of the entry consumes one session from the Tracked Object Manager‘s resource pool during a scheduled test. The Tracked Object Manager has a limit of 2000 sessions. If you configure an IP SLA entry to monitor paths, the number of sessions required for the entry increases by the product of the number of paths multiplied by the number of hops.

IP SLA also allocates 30,000 statistical entries, with each entry using approximately 240 bytes, for the distribution and history mechanisms. The statistical entry contains the data for the round-trip-time metric. The number of statistical entry resources required to start the test is dependent on the distribution count, number of paths and hops, and the number of history buckets. The calculation is as follows:

(distribution count + history buckets) * (paths * hops + 1)

For more information about the memory used by IP SLA entries and statistical entries, see System Resources Affected by IP SLA.