This Unsigned32 is the index into ClusterXL's table describing the dedicated synchronization network(s) used to replicate connection state between cluster members. Since state synchronization is what allows a failover to be seamless (existing connections surviving the switch), this index identifies which sync network entry the following Name/Addr/NetMask fields describe, relevant when a cluster uses more than one sync interface for redundancy. An admin troubleshooting connections dropping on failover (rather than surviving it) would start by checking this sync table's entries.