In deploying a number of Cisco 2960X Switch Stacks containing between 4 and 8 members I noticed many of them were logging the following message:
Failed to send hrpc non blocking message
The issue appeared after upgrading switches from 15.0(2)EX2 to 15.0(2)EX3 and persists through to at least 15.0(2)EX5. Following extensive troubleshooting both internally and with Cisco, the problem was narrowed down to the device classifier.
Whenever a switch learns a new MAC address the switch will create a new “device classifier session”. The device classifier collects information based on the MAC address vendor OUI, CDP and LLDP to identify the type of device connected to a port. Macros can then be created to perform actions based on the device type. This information is synchronised across all switches in stack. Unfortunately the switch stack cannot keep up with synchronising this information across all devices hence reports this error message.