What access and functionality do I lose when the support contract expires for a Red Hat Enterprise Linux product?

When you purchase an entitlement for Red Hat Enterprise Linux you are purchasing access to support resources and access to Red Hat Network (RHN) resources, which includes all errata and updates.

Without and active entitlement you will not receive any support or any updates.

You will still be able to log on to RHN with your account login, but will not have any active channel entitlements to receive any errata updates. The up2date command will not work because there is no channel to associate your system to.

If you log in to https://www.redhat.com/apps/support/ you can see your active entitlements and all support resources that comes with those entitlements.

You can also log on to RHN and view your RHN entitlements by clicking on the "Channels" tab at the top, then on "Channel Entitlements" link on the left hand side. You will see your current channel entitlement(s).