Review Questions

1.	Which LAN switch method runs a CRC on every frame? Cut-through Store-and-forward FragmentCheck FragmentFree
2.	Which LAN switch type checks only the hardware address before forwarding a frame? Cut-through Store-and-forward FragmentCheck FragmentFree
3.	What is true regarding the STP blocked state of a port? (Choose all that apply.) No frames are transmitted or received on the blocked port. BPDUs are sent and received on the blocked port. BPDUs are still received on the blocked port. Frames are sent or received on the blocked port.
4.	Layer 2 switching provides which of the following? (Choose all that apply.) Hardware-based bridging (MAC) Wire speed High latency High cost
5.	What is used to determine the root bridge in a network? (Choose all that apply.) Priority Cost of the links attached to the switch MAC address IP address
6.	What is used to determine the designated port on a bridge? Priority Cost of the links attached to the switch MAC address IP address
7.	What are the four port states of an STP switch? Learning Learned Listened Heard Listening Forwarding Forwarded Blocking Gathering
8.	What are the three distinct functions of layer 2 switching? Address learning Routing Forwarding and filtering Creating network loops Loop avoidance IP addressing
9.	Which of the following is true regarding BPDUs? BPDUs are used to send configuration messages by using IP packets. BPDUs are used to send configuration messages by using multicast frames. BPDUs are used to set the cost of STP links. BPDUs are used to set the bridge ID of a switch.
10.	If a switch determines that a blocked port should now be the designated port, what state will the port go into? Unblocked Forwarding Listening Listened Learning Learned
11.	What is the difference between a bridge and a layer 2 switch? (Choose all that apply.) There can be only one spanning tree instance per bridge. There can be many different spanning tree instances per switch. There can be many spanning tree instances per bridge. There can be only one spanning tree instance per switch.
12.	What is the difference between a bridge and a layer 2 switch? (Choose all that apply.) Switches are software based. Bridges are hardware based. Switches are hardware based. Bridges are software based.
13.	What does a switch do when a frame is received on an interface and the destination hardware address is unknown or not in the filter table? Forwards the switch to the first available link Drops the frame Floods the network with the frame looking for the device Sends back a message to the originating station asking for a name resolution
14.	Which LAN switch type waits for the collision window to pass before looking up the destination hardware address in the MAC filter table and forwarding the frame? Cut-through Store-and-forward FragmentCheck FragmentFree
15.	What is switching mode on a 4000 series switch? Cut-through Store-and-forward FragmentCheck FragmentFree
16.	How is the bridge ID of a switch communicated to neighbor switches? IP routing STP During the four STP states of a switch Bridge Protocol Data Units Broadcasts during convergence times
17.	How is the root port on a switch determined? The switch determines the highest cost of a link to the root bridge. The switch determines the lowest cost of a link to the root bridge. By sending and receiving BPDUs between switches. The fastest BPDU transfer rate on an interface becomes the root port. The root bridge broadcasts the bridge ID, and the receiving bridge determines what interface this broadcast was received on and makes this interface the root port.
18.	How many root bridges are allowed in a network? 10 1 1 for each switch 20
19.	What could happen on a network if no loop avoidance schemes are put in place? (Choose all that apply.) Faster convergence times. Broadcast storms. Multiple frame copies. IP routing will cause flapping on a serial link.
20.	What is the default priority of STP on a switch? 32768 3276 100 10 1

Answers

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 lowest 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 is 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 To determine the designated ports, switches use the cost of the links attached to the switch.
7.	A, E, F, H The four states are blocking, listening, learning, and forwarding. Disabled is a fifth state.
8.	A, C, E Layer 2 features include address learning, forwarding and filtering of the network, and loop avoidance.
9.	B Bridge Protocol Data Units are used to send configuration messages to neighbor switches. This includes the bridge IDs.
10.	C A blocked port always listens 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 have only one.
12.	C, D Bridges are considered software based, and switches are considered hardware based.
13.	C Switches forward all frames that have an unknown destination address. If a device answers the frame, the switch will update the MAC address table to reflect the location of the device.
14.	D FragmentFree looks at the first 64 bytes of a frame to make sure a collision has not occurred. It is sometimes referred to as modified cut-through.
15.	B The 4000 series uses the store-and-forward method for frame switching.
16.	D The bridge ID is sent via a multicast frame inside a BPDU update.
17.	B Root ports are determined by using the lowest cost of a link to the root bridge.
18.	B Only one root bridge can be used in any network.
19.	B, C Broadcast storms and multiple frame copies are typically found in a network that has multiple links to remote locations without some type of loop avoidance scheme.
20.	A The default priorities on all switches are 32768.