centos - DNF安装失败，错误提示，请问怎么办？

Question

CentOS 6.6，安装过程如下：

sudo yum install epel-release -y
sudo yum install dnf

错误提示如下：

已加载插件：fastestmirror
设置安装进程
Loading mirror speeds from cached hostfile
 * base: mirrors.zju.edu.cn
 * epel: mirror01.idc.hinet.net
 * extras: mirrors.163.com
 * updates: mirrors.zju.edu.cn
No package dnf available.
错误：无须任何处理

Answer 1

This package was not found, there is a problem with the warehouse source

Answer 2

yum install https://get.docker.com/rpm/1....