Making Xcast a Reality and Operate at the 100 Gbps Line Rate in P4 Hardware Switches

Multicast is an approach by which a packet sent by a sending host can be received by multiple receiving hosts. Traditional methods of performing multicast is via storing multicast routing information in the multicast group table of every switch (or router) on the multicast tree. When receiving a multicast packet, a switch/router will replicate the packet and forward the replicated packets out of the switch/router based on the information stored in its multicast group table. In RFC 5058, the authors proposed the concepts of Explicit Multicast (Xcast) in which the unicast addresses of the receiving hosts of a multicast group are carried in the header of the multicast packet. The concepts of Xcast were proposed in 2007 without design and implementation details for real hardware switches/routers. Recently, due to the emergence of programmable switches, designing and implementing Xcast in hardware switches becomes feasible. In this work, we design and implement an Xcast-like scheme in P4 hardware switches and evaluate its performance. Experimental results show that our scheme can multicast packets at the 100 Gbps line rate without losing any packet inside the switch due to pipeline processing backlogs.