Explanation:
From the Help file:
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Use sharing method based on
-IPs, Ports, SPIs (default) provides the best sharing distribution, and is recommended for use. It is the least "sticky" sharing configuration.
-IPs, Ports should be used only if problems arise when distributing IPSec packets to a few machines although they have the same source and destination IP addresses.
-IPs should be used only if problems arise when distributing IPSec packets or different port packets to a few machines although they have the same source and destination IP addresses. It is the most "sticky" sharing configuration, in other words, it increases the probability that a certain connection will pass through a single cluster member on both inbound and outbound directions.
Getting here - Gateway Cluster Properties > ClusterXL > Advanced

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