The bcmRX process handles traffic that is being received by the switches CPU.
When it shows a high CPU utilization when checking the "top" command this means that there is a lot of traffic being sent to the CPU (other than hardware-forwarded).
In most situations this indicates a possible loop in the network. Which commands can be used to detect a loop?
There are multiple other reasons why process bcmRX can go high, and in those cases it's best to contact TAC for further troubleshooting. How to contact Extreme Networks Global Technical Assistance Center (GTAC)