[mrtg] Re: Monitoring Gigabit Ethernet ports...

[Lars Holmström]

This has been discussed on this list before.

One limitation to keep in mind is that the default configuration file generated
by MRTG cannot accurately measure bandwidth above about 114 Mbps (Megabits per
second). The reason is that the default interface counter is a 32-bit number,
and a 32-bit number will rollover twice in a period of 5 minutes at more than
114 Mbps. (232 = 4,294,967,296 bytes, multiplied by 8 (bits in a byte), divided
by 300 seconds in 5 minutes, is 114,532,641 bits per second, or roughly 114
Mbps.) MRTG or any other SNMP program cannot correctly account for a double
rollover. The graph will appear to peak at about 114 Mbps and never go beyond
that, when in reality the interface could be running well beyond that rate. To
get around this, you must change the configuration file to pole a special 64-bit
interface counter, or poll MRTG more frequently than 5 minutes.

I do not believe the SSR has 64 bit counters.

/Lars

"Cihan Subasi (Garanti Teknoloji)" wrote:

>         Hi,
>
>         I am trying to monitor Gigabit Ethernet port usage on Cabletron
> SSR8000 chassis....Graphs seems ok when traffic is low (10-20 Mbits/s) but
> when traffic goes higher than those values graphs becomes flat (my
> understanding is because mrtg cannot get a new value from the port keeps the
> last one...Anybody every experienced similar things on Gigabit port
> monitoring? Thanks
>
> *****************************************************************
> Cihan Subasi
> Garanti Technology
> Network Services - Project Manager
> *       +90 212 478 3426
> GSM:    +90 533 2701915
> mailto:cihans at garanti.com.tr
> http://www.garantiteknoloji.com.tr
> *****************************************************************
>
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