Specifying The Probe's Period - HP 7102dl - ProCurve Secure Router Configuration Manual

Network Monitoring
Configuring Network Monitoring
9-16
The valid range for failures is from 1 to 254, and the valid range for set size is
from 1 to 255. The value for failures allowed within a set must, of course, be
smaller than the value for the set size.

Specifying the Probe's Period

The period determines how often the probe runs a test—that is, how often a
probe packet is sent out.
To set the period, from the network monitor probe configuration mode
context, enter:
Syntax: period <seconds>
For ICMP echo probes, enter a value from 1 to 65535 seconds. (If you want to
set the period to 1 second, you must first decrease the timeout because the
period must be greater than the timeout.) For TCP connect and HTTP request
probes, enter a value from 60 to 65535 seconds. For all probe types, the default
period is 60 seconds.
The period setting involves trade-offs: The shorter the period, the more
granular the picture you receive of network performance and the more quickly
an incorrect route is detected. However, shorter periods add more overhead
to WAN connections.
You can combine the settings for period, timeout (expressed in seconds, not
milliseconds), and tolerance to estimate the length of time a network would
experience unacceptable conditions before the probe notifies the track that
it has failed:
For a probe with a consecutive failure tolerance:
• (Period + Timeout) * Tolerance consecutive failures
For a probe with a rate of failure tolerance:
• (Period + Timeout) * Tolerance allowed failures (minimum)
• (Period + Timeout) * Tolerance set size (maximum)
Such a calculation might be important for a probe that is intended to monitor
the status of a route. For example, consider a configuration with a period of
10 seconds, a timeout of 1,000 milliseconds (1 second), and a tolerance of 5
consecutive failures. The sum of the period and the timeout (11 seconds in the
example) is the maximum length for a test. Multiply that maximum length by
the tolerance. In this example, the probe would detect a failed route after 55
seconds. If this time is unacceptably long, decrease the period or the tolerance.