What are two valid BPDU types? (Choose two.)
A.
topology change notification
B.
configuration change
C.
configuration
D.
root bridge
Explanation:
Topology Change Notification BPDUs
Although the majority of BPDUs on a healthy network should be Configuration BPDUs, all bridged networks see at least a few of the second type of BPDU, the Topology Change Notification (TCN) BPDU. TCN BPDUs, as their name suggests, play a key role in handling changes in the active topology. Figure 6-16 illustrates a decode of a TCN BPDU.Figure 6-16 Topology Change Notification BPDU Decode
The TCN BPDU is much simpler than the Configuration BPDU illustrated in Figure 6-15 and consists of only three fields. TCN BPDUs are identical to the first three fields of a Configuration BPDU with the exception of a single bit in the Type field. After all, at least one bit is needed to say “this is a TCN BPDU, not a Configuration BPDU.” Therefore, the Type field can contain one of two values:
0x00 (Binary: 0000 0000) Configuration BPDU
0x80 (Binary: 1000 0000) Topology Change Notification (TCN) BPDU
That’s it. TCN BPDUs don’t carry any additional information.
