sudo dnf system-upgrade download --refresh --releasever=28
Problem 2: package tcp_wrappers-devel-7.6-87.fc27.x86_64 requires tcp_wrappers-libs(x86-64) = 7.6-87.fc27, but none of the providers can be installed
- tcp_wrappers-libs-7.6-87.fc27.x86_64 does not belong to a distupgrade repository
- problem with installed package tcp_wrappers-devel-7.6-87.fc27.x86_64
This is already fixed in tcp_wrappers-7.6-91.fc28, which did not make it into beta, because it was probably not considered as important enough.
Updating to latest f28/final will work.
*** This bug has been marked as a duplicate of bug 1560757 ***