Testking_640-802_V13

Answer: C, E

Explanation:

The bridges elect a root bridge based on the bridge IDs in the BPDUs. The root bridge is the bridge with the lowest numeric value for the bridge ID. Because the two part bridge ID starts with the priority value, essentially the bridge with the lowest priority becomes the root. For instance, if one bridge has priority 100, and another bridge has priority 200, the bridge with priority 100 wins, regardless of what MAC address was used to create the bridge ID or each bridge/switch.

Reference: CCNA Self-Study CCNA ICND Exam Certification Guide (Cisco Press, ISBN 1-58720-083-X) Page 39

QUESTION NO: 12

Which of the following are spanning tree port states? (Select three answer choices)

A.Learning

B.Spanning

C.Listening

D.Forwarding

E.Initializing

F.Filtering

G.Permitting

Answer: A, C, D Explanation:

There are 4 STP states that a bridge port can be in: Blocking, Listening, Learning, and Forwarding:

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QUESTION NO: 13

What are the switch and bridge port characteristics of a layer two spanning-tree network that is fully converged?

A.All switch and bridge ports are in the forwarding state.

B.All switch and bridge ports are in the stand-by state.

C.All switch and bridge ports are assigned as either root or designated ports.

D.All switch and bridge ports are in either the forwarding or blocking state.

E.All switch and bridge are either blocking or looping.

Answer: D Explanation:

When a switch first comes up, it will be in the listening and learning states. This is needed so that the switch learns the MAC addresses of the devices on the LAN, and to learn where any loops in the network may exist. After this initial period of listening and learning, the ports will be forwarding to the hosts, or blocking certain ports that create a loop in the network. An example of this is shown below:

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In the above figure, after the network has converged, spanning tree protocol puts each port either in designated (Forwarding) or Non-designated (Blocking) state. So, Choice D is correct.

If you get a converged spanning-tree network, you have only two port states. Forwarding and Blocking. Forwarding: all traffic will be forwarded

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Blocking: all traffic to devices that will create a loop in a spanning-tree network will be blocked. It is possible to get redundant paths in large switched and routed networks.

QUESTION NO: 14

The Testking LAN consists of 6 switches connected together as shown in the diagram below:

What is the name of the potential problem of this switch setup, and what protocol can prevents its occurrence. (Select only one answer choice)

A.Routing loops, hold down timers

B.Switching loops, split horizon

C.Routing loops, split horizon

D.Switching loops, VTP

E.Routing loops, STP

F.Switching loops, STP

Answer: F

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Explanation:

The spanning-Tree Protocol (STP) prevents loops from being formed when switches or bridges are interconnected via multiple paths. Spanning-Tree Protocol implements the 802.1D IEEE algorithm by exchanging BPDU messages with other switches to detect loops, and then removes the loop by shutting down selected bridge interfaces. This algorithm guarantees that there is one and only one active path between two network devices.

QUESTION NO: 15

In a switched LAN network, what is the Spanning-Tree algorithm used for?

A.It is used to provide a mechanism for routing updates in switched environments.

B.It is used to prevent routing loops in networks with redundant routes.

C.It is used to prevent switching loops in networks with redundant switched routes.

D.It is used to manage, the addition, deletion, and naming of VLANs across multiple switches.

E.It is used to segment a network into multiple collision domains.

F.None of the above.

G.All of the above are functions of STP.

Answer: C Explanation:

To avoid loops, all bridging devices, including switches, use STP. STP causes each interface on a bridging device to settle into a blocking state or a forwarding state. Blocking means that the interface cannot forward or receive data frames. Forwarding means that the interface can send and receive data frames. By having a correct subset of the interfaces blocked, a single currently active logical path will exist between each pair of LANs. STP resides at the data link layer, so it is used to prevent loops within a switched network. It is not used to prevent routing loops; that is the function of the mechanisms within a routing protocol.

Reference:

CCNA Self-Study CCNA INTRO exam certification Guide (Cisco Press, ISBN 1-58720-094-5) page 248.

QUESTION NO: 16

In which Spanning-Tree states does a switch port learn MAC addresses? (Select two)

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A.Blocking

B.Listening

C.Forwarding

D.Learning

E.Relaying

Answer: C, D

Explanation:

STP uses a couple of port states besides forwarding and blocking.

1.Listening - Listens to incoming Hello messages to ensure that there are no loops, but does not forward traffic. This is an interim state between blocking and forwarding.

2.Learning - Still listens to BPDUs, plus learns MAC addresses from incoming frames. It does not forward traffic. This is an interim state between blocking and forwarding.

3.Disabled - Administratively down.

Reference: Cisco CCNA intro 640-821

QUESTION NO: 17

Three TestKing switches are connected together as shown in the diagram below:

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Study the Exhibit carefully. All switches have the default STP configuration and all links are Fast Ethernet. Which port on which switch will Spanning Tree place in blocking mode?

A.Switch TK1 - Port Fa1/1

B.Switch TK1 - Port Fa1/2

C.Switch TK2 - Port Fa1/2

D.Switch TK2 - Port Fa1/1

E.Switch TK3 - Port Fa1/1

F.Switch TK3 - Port Fa1/2

Answer: F Explanation:

Switch TK1 will become the ROOT BRIDGE because it has the lowest MAC address. Its both ports will become designated ports so choice A and B are wrong.

Next Election will be of ROOT PORTS. Port FA1/1 of both the switches TK2 and TK3 will become ROOT ports because they have minimum path cost to reach the root bridge. So, choices D and E are also wrong.

Next Election will be of Designated Ports on the segment connecting TK2 and TK3. TK2 has lower MAC address so, its port FA1/2 will become designated port and FA1/2 of TK3 will be placed in a BLOCKING state to avoid switching LOOPS.

QUESTION NO: 18

Four TestKing switches are connected together as shown below:

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The network shown in the exhibit was designed to provide reliability through redundancy. Both of the IDF switches, TK3, and TK4, are connected to both of the MDF switches, TK1 and TK2. Which configuration scenario will provide a loop-free switching environment?

A.Spanning Tree Protocol should be running on all switches.

B.Spanning Tree Protocol should be running on only the MDF switches TK1 and TK2.

C.Spanning Tree Protocol should be running on only the IDF switches TK3 and TK4.

D.Spanning Tree Protocol should be run only on the root bridge.

E.Spanning Tree Protocol is not needed in this network.

Answer: A Explanation:

Spanning-Tree Protocol (STP) prevents loops from being formed when switches or bridges are interconnected via multiple paths. Spanning-Tree Protocol implements the 802.1D IEEE algorithm by exchanging BPDU messages with other switches to detect loops, and then removes the loop by shutting down selected bridge interfaces. This algorithm guarantees that there is one and only one active path between two network devices.

Reference:

http://www.cisco.com/en/US/tech/tk389/tk621/tsd_technology_support_protocol_home.html

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QUESTION NO: 19

Four TestKing switches are connected together as shown in the diagram below:

Study the Exhibit carefully. What is the purpose of the Spanning Tree Protocol that is operating in the exhibited switch topology?

A.To elect a particular switch as backup designated switch.

B.To have one active Layer 2 path through the switches network.

C.To select the best path to a remote destination that is on a different network.

D.To learn the MAC addresses of host attached to the switches network.

E.To distribute VLAN configuration information throughout the switched network.

Answer: B Explanation:

Switches are connected in a way to provide full-mesh topology. So, a redundant path is provided in the case of a link or switch failure. The STP is used to prevent frames from looping throughout the network.

QUESTION NO: 20

When is a switched network that is running the Spanning Tree Protocol considered to be fully converged?

A. when all switches have the same BID as the root switch

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B.when all switches have received the MAC address of each neighboring switch

C.when every enabled switch port has been assigned a unique identifier

D.when every operating switch port is in either the blocking or forwarding state

E.when all switches are in either client, server, or transparent mode

Answer: D Explanation:

States of the Spanning Tree Protocol:

Blocking A blocked port won't forward frames; it just listens to BPDUs. All ports are in blocking state by default when the switch is powered up. The purpose of the blocking state is to prevent the use of looped paths.

Listening The port listens to BPDUs to make sure no loops occur on the network before passing data frames. A port in listening state prepares to forward data frames without populating the MAC address table.

Learning The switch port listens to BPDUs and learns all the paths in the switched network. A port in learning state populates the MAC address table but doesn't forward data frames.

Forwarding The port sends and receives all data frames on the bridged port.

Disabled A port in the disabled state does not participate in the frame forwarding or STP. A port in the disabled state is virtually nonoperational.

In Blocking States, all ports are in blocking state. The purpose of the blocking state is to prevent the use of looped paths. The forward state sends and receives the all data frames in a loop free network. So these two states are considered to be fully converged.

QUESTION NO: 21 Exhibit:

.

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