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Use the probe-backoff command to determine how aggressively the CNA system should send active probes of type TCP or ICMP to a target in the face of successive probe failures.
NOTE: The active-measurement avoid command will reduce but not eliminate probe contacts. A traceprobe is intended to locate a suitable target in place of addresses that you know in advance cannot be reached. Such proxy addresses are identified by sending a traceroute packet to the unreachable address. The last host reached before the traceroute packet fails is the host that will be probed by the CNA probing algorithm for a specified period of time; then another traceroute packet will be sent to this host, but with the TTL now set to expire upon reaching it. The resulting ICMP time exceeded message will confirm to CNA that the target is still valid. This second phase will be repeated periodically. You can prevent contact with a specified address during the CNA probing portion of the cycle by using the active-measurement avoid command, but there is no way to configure the traceroute process to avoid an intermediate hop.
The trigger value set by the probe-backoff command is not the same as the timeout value that is set when the probe is configured.
For each probe, CNA will wait for a response for the amount of time specified by the probe’s timeout value (see the target command) before considering that individual probe to have failed.
Backoff data is maintained by the CNA am-scheduler process for each probe target’s resolved IP address (one target may resolve to multiple addresses) for each USTAT.
The next time a probe is scheduled for the target, probing activity will take place normally, including the address that did not respond previously. This cycle will continue for the length of time specified by the trigger argument of the probe-backoff command.
If successive probes continue to fail over the same link for the amount of time specified by the trigger argument, probing of the target over that link will be placed in a wait state for the amount of time specified by the wait argument of the probe-backoff command.
An outage event will be reported to the CNA decision-maker process whenever a probe attempt times out, except that these reports will be suppressed if no measurements have been received from a successful probe of the prefix during the past hour. This suppression prevents the am-measurer process from inundating the decision-maker process with reports for a prefix that may not exist (an address may have been misconfigured, for example) or is no longer in use.
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