[mrtg] Re: Strange spikes with summer (router0 + router1) traffic

Larry Sheldon lsheldon at creighton.edu
Mon May 21 18:42:27 MEST 2001

I actually have no clue as to what the problem is, but I did have the 
following off-the wall conjecture while reading this . . . .

> I'm seeing these strange spikes in some summed graphs (two routers added 
> together with the + in the config). The usual traffic is in the several 
> hundred k range on each router, but occasionally there will be huge spikes 
> to 48 Mb and other very high numbers even though the graphs of the two 
> routers seperatly do not show this much traffic when added together by 
> hand. I have another summed graph of a router port and an SNMPd port on a 
> UNIX box that behaves in a similar way, but the spikes do not line up 
> time-wise between the router+router and router+server graphs.
> Most of the time the graphs show the correct traffic amounts, but it looks 
> like occasionally there will be a single sample to many megabits and then 
> it goes back to normal. This is on MRTG 2.9.10 running on a Redhat Linux 
> 7.0 box (with some of their patches installed). Does anyone have any idea 
> what might be causing these spikes and any suggestions for a possible fix?

What if the summing happens at a place that the ability to detect a counter
roll-over is lost?  (Counter roll-over handled in the individual graphs,
but not on the summed graph?)
.                                                                       .
- L. F. (Larry) Sheldon, Jr.                                            -
. Unix Systems and Network Administration                               .
- Creighton University Computer Center-Old Gym                          -
. 2500 California Plaza                                                 .
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. lsheldon at creighton.edu                  of System Administrators:     .
- 402 280-2254 (work)                Infallibility, and the ability to  -
. 402 681-4726 (cellular)               learn from their mistakes.      .
- 402 332-4622 (residence)                                              -
. http://www.creighton.edu/~lsheldon    Adapted from Stephen Pinker     .

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