Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

Using the example shown in the Protocol Overview section as a sample VLT topology, the primary VLT switch sends BPDUs to an access device (switch or server) with its own RSTP bridge ID. BPDUs generated by an RSTP-enabled access device are only processed by the primary VLT switch. The secondary VLT switch tunnels the BPDUs that it receives to the primary VLT switch over the VLT interconnect. Only the primary VLT switch determines the RSTP roles and states on VLT ports and ensures that the VLT interconnect link is never blocked.

In the case of a primary VLT switch failure, the secondary switch starts sending BPDUs with its own bridge ID and inherits all the port states from the last synchronization with the primary switch. An access device never detects the change in primary/secondary roles and does not see it as a topology change.

The following examples show the RSTP configuration that you must perform on each peer switch to prevent forwarding loops.

Configure RSTP on VLT Peers to Prevent Forwarding Loops (VLT Peer 1)

Dell_VLTpeer1(conf)#protocol spanning-tree rstp
                                 Dell_VLTpeer1(conf-rstp)#no disable
                                 Dell_VLTpeer1(conf-rstp)#bridge-priority 4096
                              

Configure RSTP on VLT Peers to Prevent Forwarding Loops (VLT Peer 2)

Dell_VLTpeer2(conf)#protocol spanning-tree rstp
                                 Dell_VLTpeer2(conf-rstp)#no disable
                                 Dell_VLTpeer2(conf-rstp)#bridge-priority 0