Gabor,
When monitoring links with speeds above 100Mbits/s you have to use the 64bit
counters.
The 32bit counters do roll over too quickly to give reliable statistics for
this link speeds.
MRTG can deal with roll overs, but is unable to see the difference between 1, 2
or more roll overs in a polling interval.
To get the 64bit counters just add :::::2 after the hostname. For details see
http://oss.oetiker.ch/mrtg/doc/mrtg-reference.en.html#item_snmpv2c
HTH,
Jan.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gabor
Sent: Monday, May 14, 2007 2:22 PM
To: [email protected]
Subject: [mrtg] MRTG accuracy issue
Dear MRTG guys,
This is my first post to this mailing list. I use MRTG to monitor
numerous things on our network. Recently an accuracy issue was brought to my
attention: MRTG shows too little traffic for Cisco Catalyst 65xx switch gig
interfaces. To test this theory, we conducted 2 tests.
Test #1: connected a sniffer to the switch (Sniffer Pro software),
monitored all traffic through gig ports and got Sniffer Pro to draw its own
graph. FYI, the sniffer was set up on a 100 Mb port but we monitored a Gig
links with no more than 60-70 Mb traffic. We found that the MRTG graph showed
roughly 30% less traffic than the Sniffer Pro graph.
Test #2: we cleared the counters on some gig interfaces. After a few
hours, then days, we checked the counters, noted the amount of traffic going
through, calculated the average and compared it to the MRTG graph. We came to
the same conclusion, namely that there was a roughly 30% difference.
For now we just consider the 30% discrepency when looking at MRTG
graphs for gig ports. It seems that MRTG is accurate for slower ports.
So, I wonder if any of you good folks have run into this problem. Is
there a special config I have to do for Gig ports or 65xx switches? I would
appreciate some thoughts, thanks in advance.
This is how I create my config:
# /usr/local/mrtg-2/bin/cfgmaker --global 'Htmldir:
/data2/web/mrtg/gig/hostname' --global 'Imagedir: /data2/web/mrtg/gig/hostname'
--global 'Logdir: /data2/web/mrtg/g
ig/hostname' --global 'RunAsDaemon: Yes' --global 'Interval: 5'
--ifref=nr --ifdesc=ip --noreversedns --global 'Options[_]: bits,growright'
--output /data2/data/mrtg/c
fgs/hostname.cfg [EMAIL PROTECTED]
A typical gig link:
### Interface 855 >> Descr: '' | Name: '1/1' | Ip: '' | Eth:
'00-01-64-75-cf-6d' ###
Target[hostname_855]: 855:[EMAIL PROTECTED]:
SetEnv[hostname_855]: MRTG_INT_IP="" MRTG_INT_DESCR=""
MaxBytes[hostname_855]: 125000000
Title[hostname_855]: 855 -- hostname.domain.name
PageTop[hostname_855]: <H1>855 -- hostname.domain.name</H1>
<TABLE>
<TR><TD>System:</TD> <TD>hostname.domain.name in </TD></TR>
<TR><TD>Maintainer:</TD> <TD>Contact info</TD></TR>
<TR><TD>Description:</TD><TD> </TD></TR>
<TR><TD>ifType:</TD> <TD>ethernetCsmacd (6)</TD></TR>
<TR><TD>ifName:</TD> <TD>1/1</TD></TR>
<TR><TD>Port Name:</TD> <TD>Gig link to Hostname</TD></TR>
<TR><TD>Max Speed:</TD> <TD>1000.0 Mbits/s</TD></TR>
</TABLE>
Sincerely,
Gabor
_____
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who are looking for what you sell.
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