The NetFlow Services Card adds NetFlow accounting to the Catalyst 4500 series. NetFlow accounting collects statistics on a per-flow basis. A flow is defined as a source IP address, destination IP address, IP protocol type, source Layer 4 port, and destination Layer 4 port. Without the NetFlow Services Card, the Supervisor Engine IV on the Catalyst 4500 does not support NetFlow accounting. The NetFlow Services Card is a configurable option on the Supervisor Engine IV for the Catalyst 4500 platform and is supported in a redundant supervisor configuration if both supervisors have a NetFlow Services Card.