net::ping throws a tcp protocol error during CPAN setup, which is what brought me to /etc/protocols and this thread.
/etc/protocols is needed or networking things break. The one I copied across from Ubuntu Hardy into TC 4.0.1 is only 239 bytes and, rightly or wrongly(?), it fixed CPAN for me.
Otherwise: could iana-etc be added as a mandatory dependency for all extensions that will need it, like Perl?