You should have a clearer idea of repository management best practises through the following examples and counterexamples.
This configuration come with maven without doing anything.
The "simple project" pom.
Without repository manager
Take a look on the "extended project" pom.
With repository manager
The "extended project" pom don't change, we just add mirrors section in the settings.xml (M2_HOME/conf/settings.xml or ~/.m2/settings.xml).
Take a look on the Mirrors definitions in settings.xml.