[rrd-users] Bits to Bytes.. trying to figure out what'shappening

Westlake, Simon simon.westlake at twcable.com
Mon Mar 19 14:58:56 CET 2007

Sorry for the top posting.. my work enforced client doesn't like to give
me any other options. Anyway..

I am actually running at a 5 minute interval which, by the calculation
you posted Alex, shows ~115 megabit per second, which was what I was
typically seeing.

I ran some quick tests, and the devices I'm monitoring all appear to
support the ifHC OID. I'm doing some further testing to ensure it won't
break any graphs, but so far, using the 64 bit counters appears to be
working fine. From the responses I've received, it appears that is
likely to be the cause of the issue (which I very much appreciate, as I
don't think I would have come to that conclusion for quite some time.)

Simon Westlake
Time Warner Cable Business Class
Network Engineer
Ph: 414.908.4791 | Cell: 414.688.7956

-----Original Message-----
From: rrd-users-bounces at lists.oetiker.ch
[mailto:rrd-users-bounces at lists.oetiker.ch] On Behalf Of Alex van den
Sent: Monday, March 19, 2007 8:46 AM
To: rrd-users at lists.oetiker.ch
Subject: Re: [rrd-users] Bits to Bytes.. trying to figure out

On Mon, Mar 19, 2007 at 09:31:42AM -0400, Dan Cech wrote:
> Westlake, Simon wrote:
> > In my gig test yesterday, I was hitting between 930 and 970 megs per
> > second on the packet generator, and the 5 minute input/output rate
> > the switch interface confirmed this to be accurate. However, my
> > show anywhere between 100 and 115 megs. At first, I wondered if it
> > some type of 'MaxBytes' problem in MRTG, so I changed that value to
> > very large amount and it didn't rectify it. I then realized that 115
> > megabytes was ~964 megabit.
> Simon,
> ~115Mbps is also around the point where you'll max out 32bit SNMP
> counters with a 1 minute polling interval, as you'll have multiple
> rollovers per minute.
> Are you using 32bit or 64bit (SNMPv2c ifHCInOctets & ifHCOutOctets)
> counters?  If you're not using 64bit counters I'd recommend switching
> them and suspect it would solve your problem.

Almost agree, except that this happens with a 5 minute polling interval:

2^32 = 4294967296
4294967296 bytes / 300 seconds =  14316557 bytes per second (Bps)
14316557 Bps * 8 bits per byte = 114532456  bits per second (bps)

Temporarily switching to a one minute polling interval (I think
you can keep "step" to 300, no problem):

2^32 = 4294967296
4294967296/60 = 71582788
71582788*8 = 572662304 -> able to monitor 570 Mbps

This buys you some time to see if and how you can use the HC counters.

Alex van den Bogaerdt

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