Abstract
IP Multicast (IPMC) in data centers becomes disruptive when the technology is used by a large number of groups, a capability desired by event notification systems. We trace the problem to root causes, and introduce Dr. Multicast (MCMD), a system that eliminates the issue by mapping IPMC operations to a combination of point-to-point unicast and traditional IPMC transmissions guaranteed to be safe. MCMD optimizes the use of IPMC addresses within a data center by merging similar multicast groups in a principled fashion, while simultaneously respecting hardware limits expressed through administrator-controlled policies. The system is fully transparent, making it backward-compatible with commodity hardware and software found in modern data centers. Experimental evaluation shows that MCMD allows a large number of IPMC groups to be used without disruption, restoring a powerful group communication primitive to its traditional role.