This is a ressurrection of a very old thread
https://fedorahosted.org/pipermail/sssd-devel/2011-July/006493.html
Compared to what Honza suggested, I'm not checking the reserverd space.
I don't think we should be babysitting the admin that much - if he wants
to use a reserved address, let him. The main point of the patch is to
skip addresses such as IPv6 Link-Local that may be present on the
interface.