Polling Bandwidth as an Aggregate

Steve Clark sclark at netwolves.com
Fri Jan 20 15:59:37 UTC 2012

On 01/20/2012 10:53 AM, Chris Adams wrote:
> Once upon a time, Leo Bicknell<bicknell at ufp.org>  said:
>> To suggest Netflow is more accurate than rrdtool seems rather strange
>> to me.   It can be as accurate, but is not the way most people
>> deploy it.
> Comparing Netflow to RRDTool is comparing apples to cabinets; one is a
> source of information and one is a way of storing information.
>> RRDTool pulls the SNMP counters from an interface and records them to a
>> file.
> No, RRDTool stores data given to it by a front end such as MRTG,
> Cricket, Cacti, etc.  That front end can fetch data from any number of
> sources, including (but not limited to) SNMP.  RRDTool then stores
> information in its database.
>> With no aggregation, and assuming your device has accurate SNMP,
>> this should be 100% accurate.  While you are right that the defaults for
>> RRDTOOL aggregate data (after a day, week, and month, approximately)
>> those aggregates can be disabled keeping the raw data.
> RRDTool does not store the raw data.  Even for 5-minute intervals, it
> adjusts the data vs. the timestamp to fit the desired interval.  Since
> you don't read every counter at the exact time of your interval, RRDTool
> is always manipulating the numbers to fit.  The only numbers that are
> not changed before storing are the timestamp and value for the most
> recent update (which get overwritten at each update); everything else is
> adjusted to fit.
I suggest reading

Stephen Clark
Director of Technology
Phone: 813-579-3200
Fax: 813-882-0209
Email: steve.clark at netwolves.com

More information about the NANOG mailing list