How to subtract a one interface from another in MRTG config

Question

I have setup MRTG for my router and I have create new target by adding all network interfaces together (lets call it Total_traffic).

I'm trying to create a new target which give total traffic expect one network interface. To do this can I subtract that particular interface from Total_traffic target? I tried use - but didn't work.

Any advice helpful, Thank you!

Answer 1

MRTG configuration does not allow you to define a Target as a function of another Target (the Routers2 frontend does allow you to display multiple Targets on one graph, or totalled, but not as more complex functions).

Instead, you need to define a new Target that makes the function you want. Make sure to surround each token with spaces.

EG:

Target[foo]: 1:comm@rtr + 2:comm@rtr + 3:comm@rtr
Target[bar]: 2:comm@rtr + 3:comm@rtr

The MRTG manual is online here; you can see the definition of the more advanced Target syntax lower down.