[rrd-users] Graphing more than 114 Mbps with RRDTool

Paul Fischer paul.fischer at cwusa.com
Mon Oct 25 18:10:40 MEST 1999


Just thought I'd pass on my knowledge before I pass on to another job. 

Problem Definition
I have been working on getting graphing working on GigEthernet and ATM
OC-12 (622 Mbps) links for several weeks. I was not able to do this in MRTG
because I thought it was rolling the numbers over on me. I was told that I
needed RRDTool to make it work. I spent many hours getting Mrtg2.8.8 and
RRDTool working, and I still was not successful.

The real problem turns out to be the SNMP OIDs I was grabbing. The default
target for MRTG and therefore RRDTool (because I used cfgmaker) is
IfInOctet&IfOutOctet. These OID's are 32-bit. This means the counters
rollover at anything more than 114 Mbps with a 5 minute polling interval. 

The Solution
One solution was to poll the router more often. I tried this with MRTG and
had problems with an Interval: of less than 5 minutes.

The solution that worked for me was to find OIDs that were 64-bits wide.
This allowed me to get the data into RRDTool before the counters rolled
over. I heard from one gent at Sun Microsystems that he was using a single
SNMP V2 OID that returned a 64-bit number. The Cisco 12000 routers I'm
using do not support that. They split the counters in two, high and low
order bits. 

My solution was to multiply the high order bits by 2^32 and add the low
order bits. I am happy to say that this worked the first time. 

My target for one ATM OC-12 PVC is shown below ( 2^32 = 4294967296). The
MIB I used is: CISCO-C12000-IF-HC-COUNTERS-MIB.my. This is an SNMP V2 MIB.

Target[abr2.8-64]: at rtr2 *
4294967296 + at rtr2

Lessons Learned
If you want to graph more than 114 Mbps you need to find a vendor specific
MIB that will give you a 64-bit variable. You will likely need a MIB Walker
to figure out which OIDs you want. I used HP Openview.

Things To Do
See if MRTG/RRDTool support exponential notation so I can use 2**32 or 2^32
instead of 4294967296.

See if MRTG will work by itself without RRDTool when graphing this target.

Get a Foundry MIB and the Foundry OIDs for my GigEthernet ports.

Make my own cfgmaker for Cisco and Foundry, and change the default OIDs to
the ones that graph more than 114 Mbps.

Buy Tobi a CD. :) (Even if he listens to wierd music)  :)

Paul Fischer - Sr. Network Eng. - Cable and Wireless Web Hosting
Author "Configuring Cisco Routers for ISDN" - Publisher McGraw-Hill
http://paul.tibex.com - paul.fischer at cwusa.com - (703) 292-2123 (v)
(703) 609-802.3 (cell) - (703) 292-2461 (fax) - Danger Will Robinson!!
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