Would you believe it's an ipv6 problem?
I'm running F12 X86_64 upgraded from F11.
The Yum problem [Cannot retrieve repository metadata (repomd.xml)] began after the F12 update and after the first yum update (installed 78 packages and updated 1742 more). THEN the (repmod.xml) problem.
I'm running off a ipv4 router so, have ipv6 disabled (I thought). But, in F12 it's different than in F11, it seems. So, here's what I did that disabled ipv6, and fixed the YUM problem. You don't need to modify /etc/hosts and all that other stuff above that didn't work for me.
1. disable the ipv6 firewall service [ipv6tables]
2. keep it off - #/sbin/chkconfig ip6tables off
3. Create a file under /etc/modprobe.d (e.g. “blacklist-ipv6.conf”) with the following 2 lines, in the order shown:
install ipv6 /bin/true
4. add the following line to /etc/sysconfig/network
(mine had IPV6=no - that don't work, but I left it in there, too)
5. reboot YUM should work fine.
---------------here's the "remove ipv6" reference-------------
Think normal human beings will ever be able to use Fedora?