Using Yum on RHEL without RHN subscription

Disable the rhn yum plugin, /etc/yum/pluginconf.d/rhnplugin.conf

[main]
enabled = 0
gpgcheck = 1

Install the epel-repo for the version of redhat you have,

RHEL 5.x

wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-5.noarch.rpm
sudo rpm -Uvh epel-release-5*.rpm

RHEL 6.x

wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm
sudo rpm -Uvh epel-release-6*.rpm

RHEL 7.x

wget https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
sudo rpm -Uvh epel-release-latest-7*.rpm

Now, you can start using yum, with the install epel repos,

sudo yum update