An administrator wants to prevent specific multicast groups defined in ACL BLOCK-MCAST from crossing from the DMZ into the internal network. Which IOS interface command applied to the internal-facing interface accomplishes this?

The ip multicast boundary BLOCK-MCAST command is used on an interface to filter outgoing multicast traffic based on the specified access list. This effectively creates a boundary, preventing multicast groups defined in BLOCK-MCAST from leaving the DMZ interface and entering the internal network. ip access-group BLOCK-MCAST in filters unicast traffic entering the interface, not multicast. ip igmp access-group BLOCK-MCAST filters IGMP messages, not the multicast data itself. no ip mroute-access BLOCK-MCAST is not a valid or relevant command for this purpose; ip mroute-access is used for controlling access to the multicast routing table, not for filtering traffic at an interface boundary.