[mrtg] MRTG log file for the OC48 not showing correct data

Yagnesh Dave yagnesh.dave at rediffmail.com
Mon Oct 12 14:03:46 CEST 2009


I am trying to get the weekly utilization by parsing through the MRTG log file for a OC48 Pos interface/ STM-16 on the router. But I have landed in a problem. While I parse through the mrtg log file and get the weekly utilization, it comes to about 2.02 %. I tried to check the real time data in the log file and converted it to bits per sec by multiplying the data in coloumn by 2 & 3 by 8, and then i verified with the graph that MRTG has plotted. Here I found that the link is actually utilised upto 30 % for In traffic while it is 13.4 % for out traffic. I am using the below calculation to get the utilised percentage. 

2.488 Gbps 
= (2.488/8) Gbps----bits/s 
= 0.311 GBps-----Bytes/s 
= 311 MBps------------------------>>>>this is the MaxByte that MRTG has 
= 311000000 Bytes/s 

Now I took about 850 samples from the log file (ignoring the first line of the log file), then took the 95th percentile of 850, which is 802 sample data, for incoming traffic in col 2, which is 8710941, and this is in Bytes/s. 

Thus, I did the following; 
8710941 Bytes/s 
= 8710941 X 8 
= 69687528 bits/sec 
= 69.687528 Mbits/sec 

Now the % utlization for the week is; 

= (8710941/311000000) X 100 
= 2.8 % 

OR if I do the cal in Mbits/s 

311000000 X 8 = 2488000000 bits/sec 


% utilization for the week is 

= (69687528/ 2488000000) X 100 

= 2.8 % 

Now, when I check in the graph that MRTG has build wih the same set of data, is as attached below, 

`Weekly' Graph (30 Minute Average) 

 Max        1568.5 Mb/s (63.0%) 
  Average  758.7 Mb/s (30.5%) 
 Current    1533.5 Mb/s (61.6%) 

 1253.7 Mb/s (50.4%) 
 332.3 Mb/s (13.4%) 
 678.3 Mb/s (27.3%) 
Please let me know where am I going wrong, or is there anything that I have missed. Please guide me. 

Yagnesh Dave. 
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