Deadlock-free multicast routing on a dragonfly network

A switch, comprising:

• an input port at which a frame is received;
• an ingress queue through which header information of the frame is passed;
• an input queue to which the frame is forwarded;
• and
• a fabric routing function receiving a routing request for the frame after arrival of the frame at the input queue, the fabric routing function being interrogated by the ingress queue using the frame's source fabric address (SFA) and destination fabric address (DFA), the fabric routing function:
• determining whether the frame is still in its source group, and whether the frame is a multicast frame;
• in response to a determination that the frame is a multicast frame, looking up the frame's SFA to determine whether multicast frames originating in the source group should be accepted or dropped.

A non-transitory computer-readable medium comprising instructions that when executed by a processor, cause the processor to:

• pass header information of a frame received at a switch port through an ingress queue;
• receive, at a fabric routing function, a routing request for the frame;
• while the header information of the frame is being processed by the ingress queue, interrogating the fabric routing function to determine whether the frame is still in its source group, and whether the frame is a multicast frame;
• in response to a determination that the received frame is a multicast frame and that the received frame is still in its source group, determining whether multicast frames originating in the source group should be accepted or dropped at the switch port where the frame was received.