A storage administrator is provisioning block storage on a new Nexus-connected server that must reach an iSCSI target array. The server's software iSCSI initiator is configured, but no LUNs appear after saving the target's portal IP address. The array requires the initiator to authenticate and dynamically learn the list of available targets from a single management portal address before mapping LUNs. Which iSCSI mechanism must the administrator ensure is functioning to allow the initiator to obtain the list of exported targets from that portal?