What are the requirements for an HA cluster to maintain TCP connections after a device failover?

The requirement for an HA (High Availability) cluster to maintain TCP connections after a device failover is to enable session pick-up. When session pick-up is enabled, it allows standby devices in the cluster to take over existing sessions seamlessly when the active device fails. This ensures that ongoing TCP connections are preserved and minimizes disruption for users and applications relying on those connections.

Session pick-up works by leveraging a shared session table or synchronization mechanism between the nodes, ensuring that the new active unit can recognize the existing sessions and maintain them without requiring a reconnection from the client side. This is particularly important for applications that rely on continuous sessions, such as VoIP or any real-time communication services.

While the other options touch on aspects of connection types and behaviors, they do not directly facilitate the maintenance of TCP connections during a failover scenario. For instance, not all types of connections, such as FTP or SMTP, relate specifically to HA and session retention capabilities; instead, they have their own protocols and requirements. Similarly, whether connections are proxied or not does not inherently determine the ability to recover TCP sessions after a failover. Lastly, session timeout settings involve connection longevity but do not play a direct role in maintaining connections post-failover.