[c-nsp] MRTG problems with STM-1, STM-4 and GE line cards on GSR

[Dean Smith]

>I'm having some obscure problems with MRTG and specific line cards on GSR.
On fastethernet line cards I'm getting normal data, also 
>data for temperature, processor utilization, memory etc. are fine on all
line cards. But on Gigabitethernet, STM-1 and STM-4 line 
>cards I'm getting really strange graphs for link utilization.

That's an SNMP counter issue.

Std Interface Byte counters are 32 Bit. If you poll every 5 mins and do the
maths, then at anything over about 114 Mbits/sec The "Bytes tx/rx" counter
actually loops once between polls. So MRTG doesn't know if its seen 120 Mb/s
or 6 Mb/s for that 5 mins.

The fix is to use the 64Bit counters introduced in SNMP V2. Should be
supported on everything by now. I don't immediately know how/if MRTG gives
access to the 64 bit counters. I would recommend moving to something like
Cacti - usess rrdtool to present the data but gives a more flexible
structured front end to create/view graphs - including the 64 bit counters.

Dean