Thanks for the swift and informative reply. I've converted this particular Target to SNMPv2c in order to get the ifHC* counters, and will monitor to see if things clear up. I verfied that the device does support ifHC* counters. Thanks again!
David On 05/02/2008, David Nolan <[EMAIL PROTECTED]> wrote: > On Feb 5, 2008 3:09 PM, David Ball <[EMAIL PROTECTED]> wrote: > > MRTG v.2.15.1 > > RRDTool v.1.2.19 (or newer..still trying to see which one is being used) > > > > I'm having problems troubleshooting an 'issue' I'm having when > > graphing in/out traffic on a GigEth interface on a Juniper router. > > For 99% of the time, it works just fine, but as per the attached .png > > image, there are times when the results MRTG gets are very low for the > > 1st value (inbound traffic). I am able to monitor the interface's > > traffic in real time and know that it rarely drops below 100Mbps > > sustained, yet for several consecutive 5min readings, MRTG shows > > rather low values. > > I'm not sure whether this is an RRDtool issue or an MRTG > > issue.....or an issue at all for that matter. Wasn't sure where else > > to look, so thought I'd try here. > > > This is a pattern I've seen many times. In fact I'd wager money that > I know exactly whats going on. > > You're collecting from a 32 bit interface counter on the router, > probably ifInOctets (1.3.6.1.2.1.2.2.1.10.*) . A 32 bit counter, > counting bytes, will roll over in under 5 minutes at approximately > 115Mbps of traffic. (2^32 / 300(seconds) * 8(convert bytes to bits) / > 1000000(convert bits to megabits) =~ 114.5). The result is that when > you collect the next data point you get a value that is only slightly > above the current value, instead of more then 2^32 above the current > value, and you have no way to know the counter rolled, and thus graph > a low value. > > The quickest fix for this, if you're only encountering it in a few > places, is collect those devices more frequently. No need to change > the rrd setup, it will handle aggregating multiple collections > together. This only works for so long though. Even if you start > collecting the data once per minute, at about 575Mbps you'll still > roll the counter.) > > The correct fix is to use a 64 bit counter, i.e ifHCInOctets > (1.3.6.1.2.1.31.1.1.1.6.*), if thats available. Most router hardware > should export that OID. However, be aware that if you just convert > from ifInOctets to IfHCInOctets, and don't have an appropriate max > value configured in RRD, you may get a huge spike on your graph. > > > -David > > _______________________________________________ > rrd-users mailing list > [email protected] > https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users > _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
