Adding local repository ( Using DVD )

1) mkdir /media/cdrom

2 ) mount /dev/cdrom /media/cdrom

3 ) create a repofile by following command

vi /etc/yum.repos.d/rhel.repo

name=Local Repository
baseurl=file:///media/cdrom
enabled=1
gpgcheck=0
#gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

Adding external repositories

1 ) cd /tmp

2) wget https://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-5.noarch.rpm

wget http://rpms.famillecollet.com/enterprise/remi-release-7.rpm

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el7.rf.x86_64.rpm
3) install the downloaded rpms

4)  sudo sed -i ‘s/enabled=0/enabled=1/g’ /etc/yum.repos.d/remi.repo

5) (optional )vi /etc/yum.repos.d/remi.repo

disable all test repositories  by setting value enabled=0

type command yum repolist to view list of repositories