A switch might be configured with spanning tree ENABLED. TRex reset the PORT at startup, making the switch reset it side as well, and spanning tree can drop the packets until it stabilizes. Disabling spanning tree can help. On CISCO nexus, you can do that using spanning-tree port type edge You can ALSO start TRex with -k <num> flag. This will send packets for k seconds before starting the actual test, letting the spanning tree time to stabilize. This issue will be fixed when we consolidate “Stateful” and “Stateless” RPC.

A switch might be configured with spanning tree enabled. TRex reset the port at startup, making the switch reset it side as well, and spanning tree can drop the packets until it stabilizes. Disabling spanning tree can help. On Cisco nexus, you can do that using spanning-tree port type edge You can also start TRex with -k <num> flag. This will send packets for k seconds before starting the actual test, letting the spanning tree time to stabilize. This issue will be fixed when we consolidate “Stateful” and “Stateless” RPC.