RSTP BPDU processing
In RSTP, a non-root bridge actively sends RSTP BPDUs at the hello time through designated ports without waiting for the root bridge to send RSTP BPDUs. This enables RSTP to quickly detect link failures. If a device fails to receive any RSTP BPDUs on a port within triple the hello time, the device considers that a link failure has occurred. After the stored configuration BPDU expires, the device floods RSTP BPDUs with the TC flag set to initiate a new RSTP calculation.
In RSTP, a port in blocking state can immediately respond to an RSTP BPDU with a lower priority than its own BPDU.
As shown in Figure 31, Device A is the root bridge. The priority of Device B is higher than the priority of Device C. Port C2 on Device C is blocked.
When the link between Device A and Device B fails, the following events occur:
Device B sends an RSTP BPDU with itself as the root bridge to Device C.
Device C compares the RSTP BPDU with its own BPDU.
Because the RSTP BPDU from Device B has a lower priority, Device C sends its own BPDU to Device B.
Device B considers that Port C2 is the root port and stops sending RSTP BPDUs to Device C.
Figure 31: BPDU processing in RSTP
