NVMoF: how to tell a command capsule from a response capsule

Question

Let's say I have RoCEv2 traffic between 2 nodes A & B.

1. A uses RDMA_SEND to send a command capsule to B.
2. Then A receives a capsule from B (B also uses RDMA_SEND). At this moment, how does A know if this is the response to its command sent in step #1, or whether this a new command capsule from B? You know, the decode will be completely different between a command and a response.

Thanks.

Answer 1

If I understand correctly, NVMeoF traffic is not symmetric. There is one node that acts as an initiator or a host, and another acting as a target or a controller. Command capsules are sent from the host to the controller, and response capsules are sent from the controller to the host.

According to the specs, each command and response includes a Command Identifier field that allows matching the command with the right response.