Can I use a Red Hat Enterprise Linux ES 3 entitlement to update a Red Hat Enterprise Linux AS 2.1 installation?

Red Hat Enterprise Linux entitlements are per family. An entitlement for Red Hat Enterprise Linux gives you access for the specific product, AS, ES, and WS no matter which version (or release) you may have specifically purchased. You will have access to the latest software available as well as supported legacy versions as long as your entitlement is active and current.

For example, Red Hat Enterprise Linux ES 2.1 and 3 or Red Hat Enterprise Linux AS 2.1 and 3 entitlements can be used to update the respective system. An entitlement for Red Hat Enterprise Linux ES gives you access to files and support for both 2.1 and 3 ES, while an entitlement for Red Hat Enterprise Linux AS gives you access to files and support for both 2.1 and 3 AS.

A Red Hat Enterprise Linux ES entitlement cannot be used for a Red Hat Enterprise Linux AS product or a Red Hat Enterprise Linux WS product.