[mrtg] MRTG Math problem

[Grossman, Benjamin]

I am getting odd (and false) spikes in a calculated graph (Target = A + B).

MRTG 2.15.2 running on Solaris 10/sparc.

I am using the 64-bit counters, so this should not be a roll-over problem as I understand it.
Normal traffic is on the order of 150Mbps on the calculated target, but shows spikes up to 300M about once per day.

Any ideas/suggestions would be appreciated, I am stumped.

CFG:
Target[sabey_isp]: #Gi1/4:XXXX at YYYY::2:1:1:2 + #Gi5/1:XXXX at YYYY::2:1:1:2
Directory[sabey_isp]: ISP
MaxBytes[sabey_isp]: 125000000
#AbsMax[sabey_isp]: 1250000000
Title[sabey_isp]:  -- SABEY ISP

Target[sabey_isp-14]:  #Gi1/4:XXXX at YYYY::2:1:1:2
Directory[sabey_isp-14]: ISP
MaxBytes[sabey_isp-14]: 125000000
AbsMax[sabey_isp-14]: 1250000000
Title[sabey_isp-14]:  -- SABEY ISP-14

Target[sabey_isp-51]:   #Gi5/1:XXXX at YYYY::2:1:1:2
Directory[sabey_isp-51]: ISP
MaxBytes[sabey_isp-51]: 125000000
AbsMax[sabey_isp-51]: 1250000000
Title[sabey_isp-51]:  -- SABEY ISP-51

LOG file extracts, showing:

Calculated (Sabey_isp):
1295913000 20375648 9171 21800861 9305
1295912700 19685784 13810 19846028 16732
1295912400 20227349 12794 20474580 16732
1295912100 21315241 23936265 21852713 39233232
1295911800 21852713 14913067 21852713 39233232
1295911500 21852713 7161 21852713 7161
1295911200 19510186 10464 21852713 12607
1295910900 19209296 24629 20010009 32534
1295910600 20836369 21413 21372142 32534
1295910300 20350011 14422 21372142 14565
1295910000 18970241 12852 19687312 14565

Actual A (Sabey_isp-14):
1295913000 4598480 182 4762068 185
1295912700 4741169 182 4762068 183
1295912400 4362711 181 4727620 183
1295912100 4382123 185 4550256 189
1295911800 4550256 189 4550256 189
1295911500 4550256 189 4550256 189
1295911200 4844603 180 5038124 189
1295910900 5323319 180 5510824 184
1295910600 5713920 182 5845598 184
1295910300 5152414 178 5845598 182
1295910000 4936158 175 5089458 177

Actual B (Sabey_isp-51):
1295913000 15782899 8989 17465649 9124
1295912700 14904615 13594 15052474 16493
1295912400 15836388 12611 16351780 16493
1295912100 16124019 12174 16351780 13546
1295911800 14747656 11838 15976350 13546
1295911500 15946386 8472 17229615 10792
1295911200 14685743 10281 17229615 12473
1295910900 13909766 24465 14499186 32350
1295910600 15122449 21230 15526544 32350
1295910300 15197597 14243 15526544 14388
1295910000 14023813 12676 14984324 14388

Benjamin k Grossman


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