| Description | The rate of packet drops of IP version cipUrpfIpVersion
packets due to URPF for the managed device. The
per-interface drop rate notification is issued on rates
exceeding a limit (rising rate). This dropping may
indicate an security attack on the network. To determine
whether the attack/event is over, the NMS must
consult the managed device. This object can be polled to
determine the recent drop rate for the managed device
as a whole, in addition to querying particular interface
objects.
This object is the average rate of dropping over the most
recent window of time. The rate is computed by dividing
the number of packets dropped over a window by the window
time in seconds. The window time is specified by
cipUrpfDropRateWindow. Each time the drop rate is computed,
and at system startup, a snapshot is taken of the latest
value of cipUrpfDrops. Subtracting from this the snapshot
of cipUrpfDrops at the start of the current window of time
gives the number of packets dropped. The drop rate is
computed every cipUrpfComputeInterval seconds. As an
example, let cipUrpfDropRateWindow be 300 seconds,
and cipUrpfComputeInterval 30 seconds. Every 30 seconds,
the drop count five minutes previous is subtracted
from the current drop count, and the result is divided
by 300 to arrive at the drop rate.
At device start-up, until the device has been up more than
cipUrpfDropRateWindow, when drop rate is computed,
the value of cipUrpfDrops is divided by the time the
device has been up.
After the device has been up for cipUrpfDropRateWindow,
when drop rate is computed, the number of packet drops counted
from interval start time to the computation time is divided
by cipUrpfDropRateWindow.
Changes to cipUrpfDropRateWindow are not reflected in this
object until the next computation time.
The rate from the most recent computation is the value
fetched until the subsequent computation is performed. |