In a ClusterXL Active-Active deployment, the Sticky Decision Function (SDF) is essential for preventing asymmetric routing. Asymmetric routing occurs when packets for the same connection are processed by different cluster members on their inbound and outbound paths. This breaks stateful inspection. The SDF ensures that a specific cluster member is designated to handle all packets for a given connection, thereby maintaining session state integrity and ensuring traffic flows symmetrically through the cluster.

A. Symmetric routing is the desired outcome that the Sticky Decision Function helps to achieve, not a problem it prevents.

B. Failover is a fundamental capability of a cluster, which SDF helps to function correctly in Active-Active mode, rather than preventing it.

D. Anti-Spoofing is a separate security feature that validates the source IP address of a packet against the gateway's topology.

1. Check Point. (2023). R81.20 ClusterXL Administration Guide. Chapter: "Load Sharing", Section: "The Sticky Decision Function".