[mrtg] Re: Question regarding Serial interface on 3725/DS3

Alex van den Bogaerdt alex at ergens.op.het.net
Fri May 7 23:26:37 MEST 2004

On Fri, May 07, 2004 at 11:00:21PM +0200, Michael Markstaller wrote:
> > Sounds like the 32 bit SNMP counter wrap issue. Try changing the top
> line in your config to use SNMPv2, allowing for 64 bit counters. Search
> the list archives for a better explanation. Use the > docs to understand
> the SNMP options.

Is it just me, or is this quote garbled for everybody?

> Garry, sorry but this wasn't a very helpful answer..
> 1. 32bit counters *could* wrap starting at ~114Mbit in 300 seconds so
> this is not the problem here with a DS3

Not quite so.  Above ~114Mbps the counter wrapping isn't noticable
anymore.  It will look as if the counters did _not_ wrap and traffic
is low.

Example numbers:

...   1234121
...   2312345 (counter has wrapped, mrtg doesn't know)
...   3123212 (counter has wrapped, mrtg doesn't know)

Below ~114Mbps the wraps will still occur.  Each time this happens,
MRTG is influenced.


...   2^32 - 12312121
...   2^32 - 23113245 (counter has wrapped, mrtg does know)
...   2^32 - 32612312 (counter has wrapped, mrtg does know)

At 6 Mbps sustained, the counters will increase with 6 * 1000 * 1000
* 300 / 8 bytes which is 225,000,000.   After 19 normal updates, the
counters _will_ wrap.  However, this means that during 19 intervals
no problem should be seen.

I think the original poster is confusing bits and bytes.

OP>The 5526.2 isn't right- but it's higher- the actual bandwidth available
OP>top end
OP>configured on the router is the ' dsu bandwidth 44210' that Bell South
OP>had me put in-

Note that 44210 divided by eight is _very_ close to 5526.2

OP>They control the speed down to 6 MB on their end to meet our SLA.
OP>MaxBytes[xxx.xxx.83.253_Serial1_0]: 5526250

If that's _really_ 6 MB (not 6 Mb) then MaxBytes should be 6,000,000 so
I guess that's not going to be true.

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