[mrtg] Re: How to draw inactive router?

Jay Hennigan jay at west.net
Tue Aug 28 09:51:18 MEST 2001

On Tue, 28 Aug 2001, Christoph Wagner wrote:

> I have devices which are sometimes not reachable (maybe because of
> power-off).
> I want to see it within MRTG. At the moment the last drawing keeps active
> and
> it is not easy to see that the values are old.

You need to do two things.

When you run cfgmaker, set the switch --no-down or --show-op-down to keep
from having the interfaces commented out when the configuration is built.
--no-down will include all interfaces whether or not they are administratively
shut down.  --show-op-down is similar but will not include those interfaces
intentionally shut down in the graphs, just those that are operationally down.

Then, in the options: section of the configuration add the keyword
"unknaszero" so that if a device is unreachable it will be shown as
zero.  The default is to repeat the last value when it was reachable
which will give you a flat line in the middle of whatever the last value
happened to be.  There are issues with this in that a single temporary
failure will be shown as a zero.  See the docs.

Read the docs for a better description of these, also check the option
"withzeroes" which you may want to set.  It affects how averages are

Note that if you are scanning a number of unreachable devices, it may take
a while for SNMP to time out, possibly more than five minutes.  This can
break things as some devices which are reachable may not get scanned.  You
might want to run multiple instances of MRTG, tweak with the SNMP timeouts,
and/or use the "forks" option (only works on UNIX) to reduce the chance
of this being an issue.

Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
NetLojix Communications, Inc.  -  http://www.netlojix.com/
WestNet:  Connecting you to the planet.  805 884-6323

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