[mrtg] High Speed If Cisco Mibs Was Re: Help--MRTG Graphing Problem

[Jérémy Lacroix]

You wrote:

I am running MRTG 2.8.12 on a Solaris 2.6 server. MRTG seems to be
working
  well with the exception that one of my router interfaces seems to be
graphing
  incorrectly. The particular interface is a high speed interface that
typically
  averages 70Mbps inbound, however, MRTG randomly reports inbound bps at
under
  1M!

  I've noticed that the inbound traffic load reaches 100-115 Mbps before

  this happens. Is there any bandwidth limitation for MRTG graphing? I
am quite
  certain that the drop in inbound traffic is false and I would like to
find out
  if anyone has a possible solution to my problem.

  Outbound bps apperars to be graphing correctly on this interface.

  Thanks in advance!

  Jeff Cates

*************

We run mrtg here on a lot of High speed interface and we noticed exactly
the same fact.
It seems coming from the Cisco Mib on several High speed interfaces.
As we're  understanding the thing, mrtg is getting ifInOctets &
ifOutOctets of the interfaces.
This OID is coded in IOS in a 16 or 24 bits, and is a counter.
mrtg is doing a Delta between Tn and Tn+1, so if the interface is
getting more octets than it can be coded in a 24 bits digits, you'll
normally get a under Zero value. However, as we understand, when the
couter is reaching a bits number higher than 110.10^6 bits/s (110 MB/s)
it flag a OID @ 1 telling it's more than 110 MB/s and add the value it
gets from ifInOctets & ifOutOctets will be add to this 110 MB/s.

The quick and dirty manner to fix the issue is to know what is the OID
which is flagged @ 1 when ifInOctets counter is going over 110 MB and
add the 110 MB value to the ifInOctet until the OID flagged to 1 is
setup back to 0.

hope this helps.


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Jeremy Lacroix, Exploit. UUNET MCI-WCOM
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Tagline for Tuesday, March 07, 2000
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