There was a bug #553017 in initscripts. ifup-eth was running '/sbin/dhcp6c' instead of '/sbin/dhclient -6'. It is fixed in rawhide (not in Fedora12).
Thanks for reply I'll try the nearest initscripts.
(In reply to comment #1) > There was a bug #553017 in initscripts. > ifup-eth was running '/sbin/dhcp6c' instead of '/sbin/dhclient -6'. > It is fixed in rawhide (not in Fedora12). Because problem is in initscripts, I'm closing this as notabug. See also Bug #559400.