I looked through my archive of portmaster-users and could only find references to external programs to fetch the snmp data which is a bit unnecessary, mrtg2.1 does maths so you can add up the requests and take off the sum ethernet ports at the end.
Having gone to the effort of looking this up thought some of you would be interested in the following line for the mrtg.cfg:
Target[pm3]: 1.3.6.1.2.1.2.1.0&1.3.6.1.2.1.2.1.0:public@pm3.domain.name - 1
This gets interfaces.ifNumber.0 which unfortunately isn't defined in the mrtg script.
Hope someone finds this useful.
Thanks to Tobias Oetiker <oetiker@ee.ethz.ch> and Dave Rand <dlr@bungi.com> for mrtg
-- Regards, Martin