Currently, an exception is raised during kickstart provisioning template rendering: https://github.com/theforeman/foreman/blob/c31702337015ecdf76aaa3053924b57007b8867f/app/views/unattended/provisioning_templates/provision/kickstart_default.erb#L135

This check should be moved closer to the MTU setting in the interface or subnet.

Source of change: https://github.com/theforeman/community-templates/commit/c68efbaf8e7f3d30cae57070716c5dc3f2b0983d

The initial change was only for kickstart; it wasn't intended to be limited to kickstart-based installations, but rather due to time constraints.