The version of perl-Net-Netmask that is in Fedora 9 is the Fedora 8 version; built for the wrong version of perl: perl-Net-Netmask-1.9015-1.fc8.noarch.rpm Please rebuild for Fedora 9.
perl-Net-Netmask-1.9015-2.fc9 has been submitted as an update for Fedora 9
perl-Net-Netmask-1.9015-2.fc9 has been pushed to the Fedora 9 stable repository. If problems still persist, please make note of it in this bug report.
It would be a good idea to add to this package: Requires: perl(:MODULE_COMPAT_%(eval "`%{__perl} -V:version`"; echo $version)) Virtually all of the perl packages have this idiom, and it ensures that the package will show up in broken dependency reports next time the perl version changes.
Re: comment#3 Paul, you may want to do this yourself if you're a Fedora maintainer; the ACLs are open and the packager seems to be busy.
Done (for devel): Task info: http://koji.fedoraproject.org/koji/taskinfo?taskID=687429