Determining when background scans run
This topic describes two important concepts for background scanning: scanning
refresh cycles and scanning windows. These concepts control when background
scans run.

Scanning refresh cycle

A scanning refresh cycle is the maximum duration (in days, weeks, or months) of a
background scan. You define separate scanning refreshcycles for discovery and for
assessment scans in a Scan Control policy. The cycles apply to the scans for all
groups that the policy controls.

Important points about refresh cycles

Refresh cycles affect scanning as follows:
vRefresh cycles apply to background discovery and background assessment scans;
they do not apply to ad hoc scans.
vAt the end of a refresh cycle, any background scanning jobs that are still running
are stopped. Their status appears as expired.
vThe refresh cycle begins at midnight on the first day of the cycle, and the jobs
for that cycle are scheduled in the Command Jobs window at that time.

Scanning windows

Scanning windows are the hours that are available for scanning each day of the
week. A scan that runs only during scanning windows pauses when a window
closes, and then resumes when the window reopens.

Scans affected by scanning windows

Scanning windows affect scans as follows:
vScanning windows apply to all background scans for the groups controlled by a
particular Scan Windows policy.
vWhen you run an ad hoc scan, you choose whether to confine the scan to the
user-defined scanning windows.

Cycle and window dependencies

Background scanning for a group requires a refresh cycle and one or more
scanning windows. Although you define refresh cycles and scanning windows in
different policies, they work together to define the extent of your background
scans. The cycle defines the duration, or elapsed time, of the scan; the scanning
windows define the days and hours when scanning may occur during the cycle.

Flexibility

Because you define refresh cycles and scanning windows in different policies, you
can use the policy inheritance properties to more precisely define your scans. For
example, you can define refresh cycles and apply the Scan Control policy to a
group with several subgroups. For each subgroup, you can define different scan
windows to control the amount of scanning on different parts of your network at
different times. For more about policy inheritance, see Chapter3, “Enterprise
Scanner policies,” on page 29.
80 Enterprise Scanner: User Guide