WebSphere® Application Server Version 7.0 is interoperable with other versions of the product under certain conditions.
Read Overview of migration, coexistence, and interoperability and Premigration considerations. For resources to help you plan and perform your migration, visit Knowledge Collection: Migration planning for WebSphere Application Server.
Interoperability applies to WebSphere administrative actions, administrative communication and to application client requests. WebSphere Application Server Version 7.0 is generally interoperable with WebSphere Application Server Version 5.1.x and Version 6.x. However, there are specific requirements to address for each version. In general, you should apply the latest fix level to support interoperability. If this is not possible, then the following interim fixes can be used to support your environment.
For web application clients, interoperability is provided by employing the HTTP server plug-in at the highest version of all of the application servers in the cell. For example, a cell comprised of WebSphere Application Server Version 7.0 and Version 6.1 application servers would use a supported HTTP server with a Version 7.0 plug-in. Refer to the TechnoteWeb server plug-in policy for WebSphere Application Server for more information.
This information is dynamic and might be augmented by information in technical articles that are available on the IBM® DeveloperWorks WebSphere site. Check the site for the latest information.