packet is sent using a multicast destination mac address in one variation the destination mac address of the loop check packet is fixed at 01 80 63 07 00 0a hex all nodes on the ring may register to receive this packet in some embodiments the packet is not transmitted to the secondary rings e g through the dual ring switches but instead only traverses the primary ring for example root node 205 transmits the loop check packet only to the rstp1 port of dual ring switch 206 not to the rstp2 port of dual ring switch 206 in some other embodiments separate loop checks may also be conducted on secondary rings one possible format for a loop check message is shown in fig4 which is explained in more detail below each node in the ring receives the packet and may manipulate the packet in various ways in step 302 the neighboring node e g dual ring switch 210 in fig2 receives the packet in step 303 if the root node is the one receiving the packet i e the packet has traversed the ring and returned to the root node then in step 304 the packet is discarded and in step 313 the ring integrity is reported to be intact assuming that the timeout time had not expired by the time the packet was received step 314 the ring integrity reporting whether success or failure may be performed in any of various ways in some embodiments an indicator light green for success red for failure may be provided in other embodiments an error message may be generated at an application level in a networked device such as a plc.