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User’s Guide – version 3.1.3 NetFlow Tracker
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U
nprocessed Flowsets
NetFlow version 9 flows are encoded in a flexible manner using templates that are
exported by the router every few seconds. For a period after starting NetFlow Tracker
or after a router reboot, flows may be received without NetFlow Tracker knowing how
t
o decode them.
Interface Scans
The software must scan the interface list of each device exporting to it whenever the
device or the software is restarted. A large number of rescans, particularly failed ones,
indicates a problem.
Missed Flows
NetFlow version 5 and 7 exports contain a sequence number to allow a NetFlow
collector to detect when exports are missed. Exports can be missed due to network
congestion or a busy router. If a switch or router is reordering the UDP packets
containing NetFlow exports you will see missed flows being registered. Note that each
export normally contains information on about 30 flows.
If the NetFlow Tracker server is under very heavy load it may drop packets itself. If you
suspect this is happening, try increasing the receive buffer size in Listener Ports
.
Missed Exports
NetFlow version 9 exports contain a sequence number to allow a NetFlow collector to
detect when exports are missed. Unlike the version 5 or 7 sequence number, this only
allows the number of missed exports to be counted rather than the number of missed
flows.
No Out Interface
The router sends flows with no out interface whenever an access control list lookup
fails or whenever multicast traffic is routed. A high number of flows without out
interfaces is normal.
No In Interface
If flows arrive with no in interface it may indicate a configuration problem on a Catalyst
switch. Please contact technical support.