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In an STP domain, which two statements are true for a nonroot switch, when it receives a configuration BPDU from the root bridge with the TC bit set? (Choose two.)
Correct Answer: B,D
Explanation/Reference: Explanation: When the TC bit is received, every bridge is then notified and reduces the aging time to forward_delay (15 seconds by default) for a certain period of time (max_age + forward_delay). It is more beneficial to reduce the aging time instead of clearing the table because currently active hosts, that effectively transmit traffic, are not cleared from the table. Once the root is aware that there has been a topology change event in the network, it starts to send out its configuration BPDUs with the topology change (TC) bit set. These BPDUs are relayed by every bridge in the network with this bit set. As a result all bridges become aware of the topology change situation and it can reduce its aging time to forward_delay. Bridges receive topology change BPDUs on both forwarding and blocking ports. An important point to consider here is that a TCN does not start a STP recalculation. This fear comes from the fact that TCNs are often associated with unstable STP environments; TCNs are a consequence of this, not a cause. The TCN only has an impact on the aging time. It does not change the topology nor create a loop. Reference: http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree- protocol/12013- 17.html#topic1