some rpm like mcrypt missing in default repository, you can't use 'yum' or download in some mirror sites

 

but you can download here

http://dl.fedoraproject.org/pub/epel/6

 

See: http://mattiasgeniar.be/2011/11/24/rhel-6-and-centos-6-missing-libmcrypt-and-libmhash-in-default-repository/