[mrtg] MRTG vs. Cricket

[McDonald, Dan]

On Sat, 2009-01-31 at 11:24 +1300, Steve Shipway wrote:
> Common problem (this really should be in an FAQ somewhere...?)
> 
> If you are polling at the default 5-min interval, a 32-bit counter will wrap at approximately 140Mbps.  Since by default MRTG will use SNMPv1 you end up using a 32bit counter unless you specify to use SNMPv2 and get the 64bit HC counters.
> 
> In your Target[] definitions, put a trailing :::::2 to specify to use SNMPv2, eg:
> 
> Target[foo]: 1:comm at device:::::2
> 
> This will use the 64bit counters, which can handle a rate of many many Gbps before wrapping, event at 5min intervals!
> 
> Another option is to use 1min intervals, but this only postpones the problem until about 700Mbps.
> 
> Always use SNMPv2 for any device supporting >100Mbps interfaces.


I don't think that's his problem, since he is using a 10-gig
interface.  

How do you know that the graphs are "off"?  Are you comparing them with
the output of "show interface" on a Cisco Router?  Show interface is an
exponentially weighted estimate of the current bandwidth utilization.
That variable is available for polling, but mrtg by default counts
actual bytes, which gives you a linear approximation of the bandwidth
used, rather than the exponentially weighted one.


> 
> Steve
> 
> ________________________________________
> From: mrtg-bounces at lists.oetiker.ch [mrtg-bounces at lists.oetiker.ch] On Behalf Of Patrick Topping [ptopping at pobox.com]
> Sent: Saturday, 31 January 2009 6:33 a.m.
> To: 'mrtg at lists.oetiker.ch'
> Subject: [mrtg] MRTG vs. Cricket
> 
> I am hoping someone can help me out with this issue I am having.....  I
> am working on migrating from Cricket to MRTG.  So far so good except
> that the Cricket graphs are pretty spot on for a 5 minute interval while
> the MRTG graphs are anywhere from 600 Mbps to 1 Gbps off at peak time.
> For example, I have a 10-gig circuit that runs roughly at 7 Gbps a peak
> time.  Cricket graphs it damn near spot on.  MRTG is off by almost a
> full gig.
> 
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-- 
Daniel J McDonald, CCIE #2495, CISSP #78281, CNX
Austin Energy
http://www.austinenergy.com

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