[mrtg] Re: Bandwidth Monitoring

[Brander, Eric]

You are probably encountering counter wrap issues.  If you are polling
32-bit SNMP counters, the counter will hit its limit (2^32) and "wrap" back
to 0 once every 5 minutes if the traffic on that interface is at
2^32/300=1,431,6558 octets (bytes) per second (109.22 Mbps). MRTG can handle
a single wrap per polling interval.  However, if you sustaining over 300
Mbps, the counter will wrap every 109.22 seconds.

This is a limitation of the SNMP Counter, NOT MRTG.

You have two options: Set your polling interval to poll more frequently and
use RRDTool (MRTG with Rateup has a minimum of 5 minute polling interval so
you must use RRDTool to poll more frequently) or use your device's 64-bit
counters.  Hopefully you can do the latter and your device has 64-bit
counters as that would be an easy fix.  With using a 64-bit counter, you
won't have a wrap problem in a 5-minute polling interval unless you exceed
469,124,961,184 Mbps. :-)

Hope this helps.

Eric Brander
ACS
Texas CHIP Account
Sr. Communications Engineer - Information Systems Department
512.336.3331
Eric dot Brander at acs-inc dot com


-----Original Message-----
From: Paul Polichronakis [mailto:paul at outsourcemail.com]
Sent: Wednesday, January 29, 2003 6:28 PM
To: mrtg at list.ee.ethz.ch
Subject: [mrtg] Bandwidth Monitoring


I have MRTG set up on a Win2000 machine to monitor 2 Cisco Routers (a
3640 and a 4500) along with 4 switches (a baynetworks 350T, and 3 Cisco
5505s).
 
I cannot seem to figure out why the machine is reporting such low
results (I have attached a link to a copy of one graph). This graph is
the interface of a 6 meg pipe that I know atleast 3 meg are being used
constantly. Does anyone have any ideas what may not be configured
correctly?
 
<img src="http://www.polynetworks.com/64.200.229.134_7-day.png">
 
http://www.polynetworks.com/64.200.229.134_7-day.png
 
Thanks,
Paul
 


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