[mrtg] Addition of counter and gauge targets

[Francesco Ferreri]

Hi all,
we have to compute the sum of the traffic flowing through several network 
interfaces, some of these interfaces can not be queried by SNMP, but they are 
defined as a GAUGE target taking its values from an external Perl script.

Is it possible to define a target which is the overall sum of COUNTER and GAUGE 
targets ? We tried to setup an example configuration:

Target[target1]: `/home/ferreri/projects/mrtg/target.pl`
Options[target1]: growright,gauge,nopercent,bits
...
Target[target2]: 2:community at router:
Options[target2]: growright,nopercent,bits
...
Target[target_sum]:`/home/ferreri/projects/mrtg/target.pl`+2:community at router:
Options[target_sum]: growright,nopercent,bits

but it seems that obtained values are completely wrong.

Any hints ?

Best regards,
Francesco Ferreri