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Chapter 4
Layer 2 Switching and the Spanning Tree Protocol (STP)
Answers to Review Questions
1.
B. Store-and-forward LAN switching checks every frame for CRC
errors. It has the highest latency of any LAN switch type.
2.
A. The cut-through method does no error checking and has the low-
est latency of the three LAN switch types. Cut-through checks only the
hardware destination address before forwarding the frame.
3.
A, C. BPDUs are still received on a blocked port, but no forwarding
of frames and BPDUs are allowed.
4.
A, B. Layer 2 switching uses ASICs to provide frame filtering and is
considered hardware based. Layer 2 switching also provides wire-
speed frame transfers, with low latency.
5.
A, C. Layer 2 devices running the STP use the priority and MAC
address to determine the root bridge in a network.
6.
B. For switches to determine the designated ports, the cost of the
links attached to the switch is used.
7.
A, E, F, H. The four states are blocking, listening, learning, and for-
warding. Disabled is a fifth state.
8.
A, C, E. Layer 2 features include address learning, forward and fil-
tering of the network, and loop avoidance.
9.
B . Bridge Protocol Data Units are used to send configuration mes-
sages to neighbor switches. This includes the bridge IDs.
10.
C. A blocked port will always listen for BPDUs to make sure that a
loop will not occur when the port is put into forwarding state.
11.
A, B. Unlike a bridge, a switch can have many different spanning tree
instances. Bridges can only have one.
12.
C, D. Bridges are considered software based and switches are consid-
ered hardware based.
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