[mrtg] Re: graphing max?

Eric Brander Eric_Mailing_List at rednarb.com
Wed Oct 27 19:59:10 MEST 2004

Mohamed S. wrote:

> How do I find out which counter im using? MRTG version 2.9.22

If your target line has ":::::2" at the end of the IP address, or if you 
specifically poll the ifHC counter's OID.

> And is that really it? I thought the ABSMAX should allow it to go higher..?

This has nothing to do with the failings of MRTG.

Since I don't want to do it over again, I'll reference another post 
here: http://www.ee.ethz.ch/~slist/mrtg/msg22220.html

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. :-)

If you need further information on counters, search the archive for 
"Counter-Wrap" and the mrtg-reference.html for "SNMPv2c".

Eric Brander

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