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User’s Guide – version 3.1.3 NetFlow Tracker
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Memory Settings
N
etFlow Tracker uses a small amount of memory during its normal operation. You can
control this amount by changing the values here, but it is not likely to be necessary.
Note that it is possible to prevent the software from working by setting inappropriate
v
alues. Note also that this page is not available on Unix installations; to change the
memory settings on Unix the “start” script must be edited.
Performance Counters
The performance counters can help diagnose problems setting up NetFlow Tracker.
Counters are stored for each device the software has received data from. The
counters are kept from when the system is started; you can reset them at any time.
Average sample storage duration
This keeps track of how long it takes the system to store a one-minute sample of real-
time data. If this takes more than about fifteen seconds it is a sign that the system is
overloaded.
Last long-term database maintenance duration
This is how long it took to perform the last update of the long-term database; if this
takes more than two to three hours you may have to reduce the number of long-term
reports you have, reduce the number of devices they cover or set some of the long-
term sample sizes to zero.
Last real-time database maintenance duration
This is how long it took to perform the last reorganisation of the real-time database;
this should not take longer than thirty minutes.
NetFlow Data Received
This counter shows the number of exports and the amount of NetFlow data received by
the software from each device. Note that this is not the amount of traffic described by
the exports but the LAN traffic generated by the exports themselves.
Traffic Described
This counter keeps track of the total amount of network traffic across all interfaces in
each direction described by NetFlow exports received from each device.
Ignored Flows
Flows are ignored if they arrive too late to be processed. If you see a large number of
ignored flows you should ensure the inactive timeout or short aging time are correctly
set as described in Appendix 1
. Some devices do not have a configurable active flow
timeout (e.g., Packeteer) and some high-end Cisco routers expose a design flaw in
NetFlow that prevents the active flow timeout from being honoured; in these cases you
can configure NetFlow Tracker to hold data in RAM for longer to prevent ignored flows
- see Database Settings
for more information.