[mrtg] Re: Flat-lining W/O Rate Drop or Outage

[Jeff Liebermann]

On Wed, Sep 20, 2000 at 11:19:45PM -0400, Jeff Hill wrote:
> Why would MRTG show a 64k ISDN connection flat-lining for short periods
> at rates of 2, 4 or 6kbps? There is no outage during these periods. 

> Graphs available at:
> http://www.hronline.com/acct_services/mrtg/205.233.215.1.16.html
> 
> Using MRTG 2.5.4 on Ascend Pipeline 50 Firmware +4.6C+

1.  Lucent/Ascend Pipeline SNMP juggles indexes every time a new
user connects.  You're graphing only some of the indexes
and ignoring all the others.  The result is that when the monitored
index loses the dice toss (or whatever Ascend SNMP uses to
elect the next index), data from this index goes to "no data
available".

It's actually worse than that as various important OID's
actually disappear and re-appear from the MIB tree when
connected and disconnected.  For some real entertainment,
run some kind of SNMPWALK utility down the entire tree
and compare the results while connected and disconnected.
You'll find about 20 or so OID's missing (it's been a while
since I did this).

To graph ALL the traffic, regardless of index, try a
Target construct such as:

Target[StovePipe50]: 2:;public at 192.168.1.254
 + 3:;public at 192.168.1.254
 + 4:;public at 192.168.1.254
 + 5:;public at 192.168.1.254
 + 6:;public at 192.168.1.254
 + 7:;public at 192.168.1.254
 + 8:;public at 192.168.1.254
 + 9:;public at 192.168.1.254
 + 10:;public at 192.168.1.254
 + 11:;public at 192.168.1.254
 + 12:;public at 192.168.1.254

The spaces at the beginning of each line are very important.

2.  MRTG has the bad habit of graphing horizontal lines, when
there is no data.  If you just pull the plug on the network
for an hour, you will get a nice flat line from whatever was
the last recorded value.  The option:
	Options[_]: UnknAsZero
was invented to fix this problem (and to get me to stop
complaining about it).

Since you were good enough to post your routers IP address,
(cali01489) I did a quick browse of your mib tree.
Index #16 (BRI Slot 1 Line 1 ) shows zero InOctets and OutOctets.
>From the URL you posted, it would appear that this is
what you're graphing.  However, I don't see any numbers.
Try the UnknAsZero option and see if the flat line stuff
goes to zero.  Otherwise, in order to display traffic, you'll
need to use use the trick I supplied.

Please change your community name to keep tourists like me
out of your machines.  Also, please drop the various PNG
and GIF files from your \mrtg-2.8.12\images\ directory
into your work directory so the pages display properly.

Weird.  I just took a closer look at your graphs.  The flat
lining is only on the incoming (blue) traffic.  The outgoing
(green) looks just fine.  I don't even have a guess what
could be causing that (exept perhaps an Ascend SNMP bug or
glitch).

-- 
# Jeff Liebermann  Liebermann Design  150 Felker St #D  Santa Cruz  CA  95060
# 831.336.2558 voice   831.426.1240 fax   831.421.6491 digital_pager
# jeffl at comix.santa-cruz.ca.us  http://www.cruzio.com/~jeffl

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