(quoted as an example)
I would not recommend just installing a package from a repository without adding the repository to your (automatic) updates. So better add the repository and then install the package. This will keep the package up to date automatically. Please check on forehand whether the repository might supersede packages already installed on your system.
FYI: The perl-NetAddr-IP package is also available from the epel package repostitory for RHEL and CentOS. (http://fedoraproject.org/wiki/EPEL
Thanks for maintaining Ispconfig 2!