1, there are many files searched by CentOS:
CentOS-5.9-x86 _ 64-bin-DVD- 1of 2 . iso
CentOS-6.4-x86 _ 64-bin-DVD 1 . iso
2.RHEL should be downloaded in official website as much as possible, or searched by file name:
rhel-server-6. 1-x86 _ 64-DVD . iso
rhel-server-6.3-x86_64-dvd.iso