Multicast Performance in FreeBSD

George V. Neville-Neil

In the past ten years most of the research in network protocols has gone into TCP, leaving UDP to languish as a local configuration protocol. While the majority of Internet traffic is TCP, UDP remains the only IP protocol that works over multicast and as such has some specific, and interesting uses in some areas of computing. In 2008 we undertook a study of the performance of UDP multicast on both 1Gbps and 10Gbps Ethernet networks in order to see if changing the physical layer of the network would give a linear decrease in packet latency. To measure the possible gains we developed a new network protocol test program, mctest, which is capable of recording packet round trip times from many hosts simultaneously and which we believe accurately represents how many environments use multicast. The mctest program has been integrated into FreeBSD and is now being used to verify the proper operation of multicast on various pieces of 10Gbps hardware.