You have to download following ISOs which will be used for deployment in the whole steps:
CentOS6.6 DVD 1
http://mirrors.aliyun.com/centos/6.6/isos/x86_64/CentOS-6.6-x86_64-bin-DVD1.iso
CentOS7.1 DVD Everything
http://mirrors.aliyun.com/centos/7.1.1503/isos/x86_64/CentOS-7-x86_64-Everything-1503-01.iso
CentOS6.5 DVD 1/2
http://vault.centos.org/6.5/isos/x86_64/CentOS-6.5-x86_64-bin-DVD1.iso
http://vault.centos.org/6.5/isos/x86_64/CentOS-6.5-x86_64-bin-DVD2.iso