checkCheck your /etc/resolv.conf/etc/resolv.conf file. YUM will check only the first nameserver, if itsit is the local DNS resolver then it will give you the error "Couldn't resolve host... "
Put onthis in your resolv.confresolv.conf nameservers as shown below:
nameserver 8.8.8.8 nameserver 8.8.4.4 (These are Google's public DNS servers.)