Beginning with version 19.2, there is a configurable ip_cache_expiry timeout that can be set from the web UI: System > Global Settings > Cache Settings. This applies to Universal, J2EE and Source IP address-based session persistence types.
This allows setting an expiry time on cached session maps which may help to redistribute load between pool nodes when new nodes are added, or when nodes recover from a failure. This is especially true in enterprise environments where the set of clients might be fixed. Configuring a session cache with a limited lifespan can also help when placing nodes into a draining state.
Cache size and expiry settings are global - the value you set applies equally to all Session Persistence class instances you create for a particular persistence method.
The Traffic Manager does not actively delete cache entries when they reach the defined expiry time. Instead, the cache entry time is checked against the expiry value only when the entry is looked up. If the session is still current, the Traffic Manager returns the session and resets the cache entry time for that session mapping. If the session is deemed expired, the Traffic Manager deletes it from the cache and establishes a new session.
NOTE: To optimally set the IP cache size and expiry values may require monitoring the cache behavior using the Activity Monitor. For more details and steps to monitor, please refer to the vTM User Guide 19.2 or higher, section 'Configuring Session Persistence Caches'