By setting an option on the SSL server, it can cache the SSL session (identified by its session ID) for a specified period of time after a given connection between the SSL client and server has terminated. During this specified period of time, if the same SSL client attempts to reconnect to this SSL server and requests a resumption of a previous SSL session (by ID), the usual authentication and hand-shaking required to establish an SSL session is dispensed with, and the SSL server reactivates the SSL session that is cached from the previous connection with this same client.
All the session components that were used in the previous connection are reused for this new connection except for those that are unique to a given connection (see
Keys and certificates). This helps to minimize negative SSL performance impacts.