[mrtg] Re: Cisco Switch: Interfaces don't add up right

[Koelstra, J. (Jan)]

Hi Shane,

I suspect you don't use the 64-bit counters but the default 32-bit counters in the MRTG config file.
See http://people.ee.ethz.ch/~oetiker/webtools/mrtg/mrtg-reference.html#item_version for details.

To change to 64-bit counters using configmaker have a look at http://people.ee.ethz.ch/~oetiker/webtools/mrtg/cfgmaker.html#item__2d_2dsnmp_2doptions__3a_5bport_5d_5b_3a_5btimeout

Hth,

Jan.

-----Original Message-----
From: mrtg-bounce at list.ee.ethz.ch [mailto:mrtg-bounce at list.ee.ethz.ch] On Behalf Of Shane Presley
Sent: Thursday, April 07, 2005 2:46 PM
To: mrtg at list.ee.ethz.ch
Subject: [mrtg] Cisco Switch: Interfaces don't add up right


Hello,

We're using MRTG to watch a 26 port Cisco switch. It has 24 100mb ports, and 2 1000mb ports.  Basically the 100mb ports are connected to Unix servers, and the 1000mb ports are uplinks connected to our backup media servers (for tape backup).  So each night our servers back themselves up by sending data to the uplink port (where the media server is)

The MRTG configs look right.  It detected the 24 ports as 12.5MB/s and the uplinks as 125MB/s.

When we fire off our backups at midnight, we see lots of ports max out (95% utilization or about 11MB/s).  They all are sending data to our uplink port (media server).  But what's odd is the gigabit uplink port only shows 10% utilization (11MB/s).

Since we have multiple ports sending data at exactly the same time
(midnight) and MRTG accurately reflects this, we expected to see an aggregate bandwidth to the uplink of about 40MB/s.  If you look at the graphs and add up the various servers sending 11MB/s in, how can the uplink also only be doing 11MB/s out.

Sorry if that's a little confusion, wasn't sure how to explain it.

Thanks,
Shane

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