MRTG as it is distributed contains several perl modules created by other
people.

The Plain Perl SNMP Code from Simon Leinen <simon@switch.ch>

  SNMP_Session.pm
  BER.pm

  --> http://www.switch.ch/misc/leinen/snmp/perl/

The SNMP Utilities module from Mike Mitchell   <Mike.Mitchell@sas.com>

  SNMP_util.pm
  
  --> this is distributed together with SNMP_Session.pm

The PodParser Module from Brad Appleton  <bradapp@enteract.com>

  Pod/*.pm

  --> CPAN/modules/by-module/Pod/BRADAPP/ (Included with perl 5.6)

Thanks very much
tobi