To reconfigure CPAN:

% towel root # perl -MCPAN -e shell

cpan shell -- CPAN exploration and modules installation (v1.59_54)
ReadLine support available (try 'install Bundle::CPAN')

cpan> o conf init

/usr/lib/perl5/5.6.1/CPAN/Config.pm initialized.

CPAN is the world-wide archive of perl resources. It consists of about
100 sites that all replicate the same contents all around the globe.
Many countries have at least one CPAN site already. The resources
found on CPAN are easily accessible with the CPAN.pm module. If you
want to use CPAN.pm, you have to configure it properly.

If you do not want to enter a dialog now, you can answer 'no' to this
question and I'll try to autoconfigure. (Note: you can revisit this
dialog anytime later by typing 'o conf init' at the cpan prompt.)

Are you ready for manual configuration? [yes]