[mrtg] Re: Help with 3COM router

[Alex van den Bogaerdt]

Andrew MJ. Pike wrote:
> 
> We are using mrtg on a 3Com router. The problem is that we are only
> measuring 480 kbps, where our upstream provider is showing us as using
> between 3-4mbps.
> 
> Any ideas? Could it be a counter issue where the counter is rolling
> over? The unit is set to poll every 5 mins, and it is on a 100mbps
> circuit.

This roll over would happen at 2^32 / 300 = 14,316,557 bytes/second.
Not even close to what the provider is reporting.

In another mail you already said it is not a bits vs. bytes problem.

That leaves (I think) three possibilities:

1) the provider multiplies by 8 two times
2) your router doesn't report correct stats
3) your mrtg configuration doesn't show the stats properly


How I would investigate:

Try to saturate your line.  When the line is fully utilized,
you know what it should transfer.

Now fetch the counters using snmpget / snmputil / whatever other
utility you have around.  The OIDs to monitor are
   1.3.6.1.2.1.2.2.1.10.<instance number>
   1.3.6.1.2.1.2.2.1.16.<instance number>

make sure you're looking at the right instance.  You probably
can do this by looking (once) at 1.3.6.1.2.1.2.2.1.2.<instance>
and comparing the description to what you think it should be.

Suppose your router is on a 5 Mbps link.  Also suppose the right
instance to monitor is 1 and the line is saturated.  When I'd run
the following script ...

    snmpget router public 2.2.1.10.1 2.2.1.16.2
    sleep 60
    snmpget router public 2.2.1.10.1 2.2.1.16.2

... I'd expect an increase of 60*5,000,000/8 = 37,500,000 bytes
(it will be a bit lower probably).

When you can saturate the link for 10 minutes, you can be sure
at least one MRTG interval shows near the maximum capacity.
This helps you determine which side is wrong and if it's your
side, where it goes wrong.

HTH
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