Bits in Overall peering graphs

[bcix]

Hey,

when I compare the In- and Out-bits in the "Overall peering graphs",
numbers are different to the values which a generated by MRTG itself in the "ixp_peering-bcix-total-bits.html" file.

See the two screenshots attached. Feature or Bug ?

Cheers, Thorleif

[nickhilliard]

"Feature or Bug?" Yes.

IXP Manager parses mrtg log files and picks out slightly different values for the graphs than standard mrtg.

For the daily 5 minute graph, ixp manager selects the actual reading over the previous 300 second sample interval (i.e. second line of log file), whereas mrtg picks up the third line. There are similar differences for the weekly / monthly / annual graphs.

It's been a couple of years since I've looked at this code and I remember being frustrated at the time about the lack of documentation for how mrtg calculated these values. The code is in Mrtg.php if you want to take a look at it. I think it's correct, although I do understand that it is usually slightly (but not very much) different to the values that stock mrtg provides.