Which protocol is often required for multicast data flow among a group of servers?

The correct protocol for multicast data flow among a group of servers is Internet Group Management Protocol (IGMP). IGMP is specifically designed to manage the membership of Internet Protocol multicast groups. When applications on multiple servers or clients need to receive the same data simultaneously, IGMP helps in establishing and maintaining the membership of these multicast groups within a local network.

IGMP operates between hosts and neighboring multicast routers, allowing hosts to inform the router of their multicast group memberships. When a multicast packet is sent, IGMP ensures that all hosts interested in that multicast group can receive the data by informing the router which multicast addresses should be forwarded.

In contrast, the other protocols do not serve this function. Address Resolution Protocol (ARP) is used for resolving IP addresses into MAC addresses rather than managing multicast traffic. Reverse ARP (RARP) is designed for providing an IP address to devices that only know their MAC address, which is not related to multicast communication. Internet Control Message Protocol (ICMP) is used for sending error messages and operational information regarding network conditions but does not handle multicast group management. Therefore, IGMP is the appropriate choice for managing multicast data flows.