When you run a yum command like:

yum install vim

You may get the following error:

Loaded plugins: fastestmirror
http://repo.dimenoc.com/pub/centos/7.1.1503/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not Found
Trying other mirror.
Is this ok [y/d/N]: y
Downloading packages:
Delta RPMs disabled because /usr/bin/applydeltarpm not installed.
vim-enhanced-7.4.160-1.el7.x86 FAILED
http://ftp.linux.ncsu.edu/pub/CentOS/7.1.1503/os/x86_64/Packages/vim-enhanced-7.4.160-1.el7.x86_64.rpm: [Errno 14] HTTP Error 404 - Not Found

To fix the error:

yum clean all
yum update

Now try again:

yum install vim

The command should continue normally.