How much bandwidth netflow export uses

Question

Experts,
I tried searching doc on cisco and even googled for information on how much bandwidth netflow export uses; however I didn't find any convincing article. I also found lancope.com where they estimate the BW required, but still I was not satisfied.
I would really appreciate if someone can guide me with simple yet affective explanation or say rough guide lines to estimate the bandwidth used by netflow exports...
Regards,
Smitesh

Answer 1

yeah this number is so hard to define, because it really is dependent on the flow export timers, active/inactive, how long flows are active or inactive and also very importantly the cache size.
generally netflow aggregators (aka routers) use a cache and start to aggressively age out flows when the cache utilization reaches a certain level.
Also if you have long lived flows and a few of them and a cache size that accomodates it, the export rate is merely defined by the active timer.
If you have a lot of flows, relative smaller cache, you will automatically see more BW util.
If you have a lot of short lived flows, then the inactive timer will come into play here.
to sum it up, a record generally takes 300 bytes (somewhat), if you use v9, then you'll also see template exports.
all in all, netflow export is generally bursty, but very much related to the traffic patterns also.
Since this number is so specific to your scenario, best to do is to set up a qos pmap that matches on your netflow export, and use the qos mib to average the rate on that class to see how it looks like for you.
To pre-estimate something, you'll need at minimum: cache size, number of flows, flow duration (so you can correlate that towards the active vs inactive timers) and the timers itself. That all multiplied against the record size, this just to get a ballpark number.
cheers
xander
xander thuijs CCIE#6775
Principal Engineer ASR9000/XR SW group