NetFlow impact on hardware performance carries a common misconception. Competitors of Cisco would like you to believe that enabling NetFlow will often bring the router or switch to its knees. The sFlow founders would also like you to believe this. Although we are sFlow supporters, I thought I would take an opportunity to set the record straight. 

In general, most customers see only a very slight CPU increase (i.e. 2% – 3%) on routers when NetFlow is enabled. I decided to investigate this topic further. Here is what Cisco has to say about the impact NetFlow has on performance  (see slide 74 & 75).

  • Enabling NetFlow version 5 AND exporting increases the cpu utilization by around 15 % (with a max of 20 % depending on the platform)
  • Enabling Neflow version 8 increases the cpu utilization by 2 to 5%, depending on the number of aggregations enabled With a multiple of 6% for multiple aggregations
  • NetFlow is done in hardware on the cat6000 supervisor and the 12000 Engine 3 Line Cards

Like sFlow switches, Enterasys switches perform NetFlow exports using hardware with no impact to the CPU. Some vendors would like us to believe that NetFlow always impacts hardware performance. It simply isn’t true.

Mike Patterson author pic


Michael is one of the Co-founders and the former product manager for Scrutinizer. He enjoys many outdoor winter sports and often takes videos when he is snowmobiling, ice fishing or sledding with his kids. Cold weather and lots of snow make the best winters as far as he is concerned. Prior to starting Somix and Plixer, Mike worked in technical support at Cabletron Systems, acquired his Novell CNE and then moved to the training department for a few years. While in training he finished his Masters in Computer Information Systems from Southern New Hampshire University and then left technical training to pursue a new skill set in Professional Services. In 1998 he left the 'Tron' to start Somix which later became Plixer.


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