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New Member

Netflow on a Sup720 Version 2

So my next question; now that I have Netflow collection properly configured - how can I limit the amount of CPU it can use? THE NDE process can hit pretty hard on the CPU; most of the good stuff happens in hardware anyway so I'm okay with some CPU utilization spent on this but I have a money making network. I need to ensure that the NDE process CAN'T overrun the router. Is there a way to limit the amount of processor a process can hog up?

4 REPLIES
Cisco Employee

Re: Netflow on a Sup720 Version 2

Here's some info that might be helpful:

It is important to look at timers and exports as aggressive timers will lead to frequent purging of netflow table and frequent export of netflow entries to the collector.

Default timers result in optimal cpu usage, but it also depends on the traffic that you have in the network.

For example:

One must understand several characteristics of the traffic in the network, including average packets/second of throughput and average number of packets/flow, to estimate the amount of data Netflow will generate.

For example, if the average throughput on a Cisco

7600 router is 150kpps and the average number of packets per flow is 20, the device will

forward about 7500 flows per second. One can then expect 250 flow export datagrams (v5 in

this example) per second (7500 flows/30 flows per export datagram), or about 250 x 1500

bytes/datagram = 375KB/second of flow export traffic from one router toward the collector.

So a lot depends on traffic flow in the network , so it is hard to say how much CPU will

increase by enabling netflow. It can vary from one device to another.

New Member

Re: Netflow on a Sup720 Version 2

How might I make these calculations on my own router?

New Member

Re: Netflow on a Sup720 Version 2

I came across this Cicso white paper titled "Netflow Performance Analysis". It may provide some information regarding your request for CPU impact.

http://www.cisco.com/en/US/customer/tech/tk812/technologies_white_paper0900aecd802a0eb9.shtml

Regards,

-m2

New Member

Re: Netflow on a Sup720 Version 2

Dude, that's a pretty awesome article - I just wish it has a sup720 in there. How can I calculate how many flows per minute other than the obvious of just watching the counter?

Also; do I need to watch the CPU on the individual cards? "Execute-on" doesn't appear to work the same as on a 12000 on the sup720.

Thanks!

-Mike

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