Which statement is true about RSTP topology changes?
A.
Only nonedge ports moving to the blocking state generate a TC BPDU.
B.
Any loss of connectivity generates a TC BPDU.
C.
Any change in the state of the port generates a TC BPDU.
D.
Only nonedge ports moving to the forwarding state generate a TC BPDU.
E.
If either an edge port or a nonedge port moves to a block state, then a TC BPDU is generated.
Explanation:
The IEEE 802.1D Spanning Tree Protocol was designed to keep a switched or bridged network
loop free, with adjustments made to the network topology dynamically. A topology change typically
takes 30 seconds, where a port moves from the Blocking state to the Forwarding state after two
intervals of the Forward Delay timer. As technology has improved, 30 seconds has become an
unbearable length of time to wait for a production network to failover or "heal" itself during a
problem.
Topology Changes and RSTP
Recall that when an 802.1D switch detects a port state change (either up or down), it signals the
Root Bridge by sending topology change notification (TCN) BPDUs. The Root Bridge must then
signal a topology change by sending out a TCN message that is relayed to all switches in the STP
domain. RSTP detects a topology change only when a nonedge port transitions to the Forwarding
state. This might seem odd because a link failure is not used as a trigger. RSTP uses all of its
rapid convergence mechanisms to prevent bridging loops from forming.
Therefore, topology changes are detected only so that bridging tables can be updated and
corrected as hosts appear first on a failed port and then on a different functioning port.
When a topology change is detected, a switch must propagate news of the change to other
switches in the network so they can correct their bridging tables, too. This process is similar to the
convergence and synchronization mechanism-topology change (TC) messages propagate through
the network in an everexpanding wave.