What configuration setting prevents a packet sniffing program from analyzing network packets on a virtual switch?

Setting Promiscuous Mode to Reject on a virtual switch is the correct configuration to prevent a packet sniffing program from analyzing network packets. When Promiscuous Mode is set to Accept, the virtual switch allows the virtual network adapter of a virtual machine to receive all packets on the network segment, regardless of their destination. This includes not only packets addressed to the virtual machine but also those meant for other machines. Consequently, a packet-sniffing program running on any virtual machine connected to the same virtual switch could capture sensitive data that it shouldn't have access to.

By configuring Promiscuous Mode to Reject, the virtual switch blocks the virtual machines from receiving packets that are not specifically addressed to their virtual NICs (Network Interface Cards). This enhances the security of the network environment by preventing unauthorized access to packet data, thus making it significantly more difficult for packet sniffing tools to capture and analyze traffic not intended for them. This setting is particularly important in environments where security and data integrity are critical.