Library catalog VMs sit on two different ESXi clusters and must share one NSX segment. Which SDN building block sets the maximum span of that segment?

For library catalog virtual machines that must share one NSX segment across two ESXi clusters, the transport zone is the SDN building block that sets the maximum Layer-2 span. Membership in the same overlay or VLAN transport zone is what authorizes prepared hosts—and therefore any catalog VMs that land on those hosts—to attach to that segment. Think of the transport zone as the city’s official map of which prepared streets may connect to the same virtual hallway: if a library host is outside the zone, the segment simply does not exist there, no matter how healthy the cluster looks. A vSphere resource pool only partitions CPU and memory shares; it never becomes a Layer-2 boundary and cannot stretch a broadcast domain between clusters. A Horizon desktop pool publishes desktops or applications for end users and does not define NSX segment span. A Carbon Black sensor group organizes endpoint agents for isolation or policy and is unrelated to NSX fabric membership. Exam caveat: transport-zone type still matters—overlay zones back Geneve segments and VLAN zones back VLAN-backed segments—but the exam ask here is the span construct itself, not the encapsulation recipe. Segment reach is limited to transport nodes in that zone; clusters alone are not the span object. Operational check: confirm every ESXi host that might host a library catalog VM is prepared as a transport node in the intended transport zone; attach a test VM on each cluster to the same segment and verify L2 adjacency (for example ARP or ping) while a host left out of the zone cannot attach the segment in inventory.