[mrtg] sum router interface (SNMP)

[Steve Shipway]

> I'm tracking several router interfaces with mrtg for the traffic. The
> graph shows the in and out data, I would like to additionally see a sum
> of both in and out in the graph.
> Is it possible to get the sum within the mrtg configuration or do I need
> to write a script of my own?

You have two options (well, three, if you count creating your own script):

* In native MRTG, you can define a calculated target - eg,
Target[sum]: 1:comm at router + 2:comm at router
And then get a graph showing the total of multiple targets.  This works in all MRTG modes, but you only get a single line on the graph so no breakdown of the components.

* If you are using RRDtool and the routers2 frontend, you can define a userdefined summary graph over the component Targets.  This allows you to have all the lines on a single graph, plus a total and/or average line.  You can also do clever things like stack the component lines, or put 'incoming' above the x-axis and 'outgoing' below the x-axis, or even do all these things at the same time.
Example:
http://www.steveshipway.org/cgi-bin/routers2.pl?rtr=switches%2Fswitch.cfg&xgtype=d&if=_incoming

Steve