[mrtg] False Graph

Steve Shipway s.shipway at auckland.ac.nz
Wed Feb 3 22:12:40 CET 2010

> > I'm also facing terrible problem with mrtg false graph. I hv attached
> > WAN gigabit interface of cisco router. When bandwidth over 200 Mbits/s
> > , graph goes false. When i monitor real time, it show nearly
> > 300Mbits/s in router. I use SNMP version 1 for mrtg as well as my
> > router

This is a known problem with using SNMPv1.  

When using SNMPv1, the 16 bit counters will roll over within 5minutes if the throughput is over about 140Mbps.

You have two options:

1. Increase polling to every 1minute instead of every 5mins.  This will mean deleting all your old RRD files, and will let you get up to about 700Mbps before you hit the problem again.  Also, you cant do this unless you are using MRTG in RRDtool mode.

2. Use SNMPv2 which uses 64bit counters and so does not have rollover problems.

Option 2 is by far the best option to use.


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