[mrtg] cisco switches, etherchannel, and artificially low graph values?

Kettler, Matt Matt.Kettler at edocorp.com
Fri Mar 21 17:32:38 CET 2008

The 64-bit counter rollover is likely the problem here. I've regenerated
my config and we'll see how it goes. Thank you both Jan and Dan.


Also, thanks for the ifref tip. This helps me not with this problem, but
with another problem I've got where my router re-enumerates interfaces
when it reboots. (I know this isn't the problem with my switch, as it
hasn't rebooted, and I already tried regenerating the config, without it
being fixed.)





From: Koelstra, J. (Jan) [mailto:JKoelstra at MINSZW.NL] 
Sent: Friday, March 21, 2008 11:31 AM
To: Kettler, Matt; mrtg at lists.oetiker.ch
Subject: RE: [mrtg] cisco switches, etherchannel,and artificially low
graph values?




It looks like your config is not using the 64bit counters but the 32bit
counters. At about 114Mbits/s the 32bit counters roll over once per 5
minutes. MRTG can deal with one roll over per interval but there is no
way to deal with multiple roll overs.

Resent versions of MRTG detect the availability of the ifHC* (i.e.
64bit) counters. In the older versions you need to specify the usage of
the 64bit counters in the cfgmaker command: --snmp-options=:::::2

You can also manualy add the :::::2 at the end of the targetlines in the
mrtg cfg file to get the 64bit counters.


An other possibility is that the ifIndex for the specific port has
changed, and now you are looking at an graph with figures from an other
port. This can easily happen after changes in the configuration. 

To fix an interface to one graph you can add '--ifref=name' or
'--ifref=descr' in the cfgmaker command.







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