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Passleader Cisco 200-120 Study Materials Covers All Knowledge Points Of Real Exam Ensure 100 Percent Pass (21-30)

QUESTION 21
Which command enables RSTP on a switch?

A.    spanning-tree uplinkfast
B.    spanning-tree mode rapid-pvst
C.    spanning-tree backbonefast
D.    spanning-tree mode mst

Answer: B
Explanation:
Ethernet network is a shared environment so all devices have the right to access to the medium. If more than one device transmits simultaneously, the signals collide and can not reach the destination. If a device detects another device is sending, it will wait for a specified amount of time before attempting to transmit. When there is no traffic detected, a device will transmit its message. While this transmission is occurring, the device continues to listen for traffic or collisions on the LAN. After the message is sent, the device returns to its default listening mode.

QUESTION 22
What is the function of the command switchport trunk native vlan 999 on a Cisco Catalyst switch?

A.    It creates a VLAN 999 interface.
B.    It designates VLAN 999 for untagged traffic.
C.    It blocks VLAN 999 traffic from passing on the trunk.
D.    It designates VLAN 999 as the default for all unknown tagged traffic.

Answer: B
Explanation:
Configuring the Native VLAN for Untagged Traffic
A trunk port configured with 802.1Q tagging can receive both tagged and untagged traffic. By default, the switch forwards untagged traffic in the native VLAN configured for the port. The native VLAN is VLAN 1 by default.

QUESTION 23
Why will a switch never learn a broadcast address?

A.    Broadcasts only use network layer addressing.
B.    A broadcast frame is never forwarded by a switch.
C.    A broadcast address will never be the source address of a frame.
D.    Broadcast addresses use an incorrect format for the switching table.
E.    Broadcast frames are never sent to switches.

Answer: C
Explanation:
Switches dynamically learn MAC addresses based on the source MAC addresses that it sees, and since a broadcast is never the source, it will never learn the broadcast address.

QUESTION 24
Which two link protocols are used to carry multiple VLANs over a single link? (Choose two.)

A.    VTP
B.    802.1q
C.    IGP
D.    ISL
E.    802.3u

Answer: BD
Explanation:
Cisco switches can use two different encapsulation types for trunks, the industry standard 802.1q or the Cisco proprietary ISL. Generally, most network engineers prefer to use 802.1q since it is standards based and will interoperate with other vendors.

QUESTION 25
Assuming the default switch configuration, which VLAN range can be added, modified, and removed on a Cisco switch?

A.    1 through 1001
B.    2 through 1001
C.    1 through 1002
D.    2 through 1005

Answer: B
Explanation:
VLAN 1 is the default VLAN on Cisco switch. It always exists and can not be added, modified or removed.
VLANs 1002-1005 are default VLANs for FDDI & Token Ring and they can’t be deleted or used for Ethernet.


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QUESTION 26
Which statement about VLAN operation on Cisco Catalyst switches is true?

A.    When a packet is received from an 802.1Q trunk, the VLAN ID can be determined from the source MAC address and the MAC address table.
B.    Unknown unicast frames are retransmitted only to the ports that belong to the same VLAN.
C.    Broadcast and multicast frames are retransmitted to ports that are configured on different VLAN.
D.    Ports between switches should be configured in access mode so that VLANs can span across the ports.

Answer: B
Explanation:
Each VLAN resides in its own broadcast domain, so incoming frames with unknown destinations are only transmitted to ports that reside in the same VLAN as the incoming frame.

QUESTION 27
Which three statements about RSTP are true? (Choose three.)

A.    RSTP significantly reduces topology reconverging time after a link failure.
B.    RSTP expands the STP port roles by adding the alternate and backup roles.
C.    RSTP port states are blocking, discarding, learning, or forwarding.
D.    RSTP provides a faster transition to the forwarding state on point-to-point links than STP does.
E.    RSTP also uses the STP proposal-agreement sequence.
F.    RSTP uses the same timer-based process as STP on point-to-point links.

Answer: ABD
Explanation:
One big disadvantage of STP is the low convergence which is very important in switched network. To overcome this problem, in 2001, the IEEE with document 802.1w introduced an evolution of the Spanning Tree Protocol: Rapid Spanning Tree Protocol (RSTP), which significantly reduces the convergence time after a topology change occurs in the network. While STP can take 30 to 50 seconds to transit from a blocking state to a forwarding state, RSTP is typically able to respond less than 10 seconds of a physical link failure.
RSTP works by adding an alternative port and a backup port compared to STP. These ports are allowed to immediately enter the forwarding state rather than passively wait for the network to converge.
RSTP bridge port roles:
* Root port – A forwarding port that is the closest to the root bridge in terms of path cost
* Designated port – A forwarding port for every LAN segment
* Alternate port – A best alternate path to the root bridge. This path is different than using the root port. The alternative port moves to the forwarding state if there is a failure on the designated port for the segment.
* Backup port – A backup/redundant path to a segment where another bridge port already connects. The backup port applies only when a single switch has two links to the same segment (collision domain). To have two links to the same collision domain, the switch must be attached to a hub.
* Disabled port – Not strictly part of STP, a network administrator can manually disable a port

QUESTION 28
At which layer of the OSI model is RSTP used to prevent loops?

A.    physical
B.    data link
C.    network
D.    transport

Answer: B

QUESTION 29
What does a Layer 2 switch use to decide where to forward a received frame?

A.    source MAC address
B.    source IP address
C.    source switch port
D.    destination IP address
E.    destination port address
F.    destination MAC address

Answer: F
Explanation:
When a frame is received, the switch looks at the destination hardware address and finds the interface if it is in its MAC address table. If the address is unknown, the frame is broadcast on all interfaces except the one it was received on.

QUESTION 30
Which two benefits are provided by creating VLANs? (Choose two.)

A.    added security
B.    dedicated bandwidth
C.    provides segmentation
D.    allows switches to route traffic between subinterfaces
E.    contains collisions

Answer: AC
Explanation:
A VLAN is a switched network that is logically segmented on an organizational basis, by functions, project teams, or applications rather than on a physical or geographical basis.
Security:
VLANs also improve security by isolating groups. High-security users can be grouped into a VLAN, possible on the same physical segment, and no users outside that VLAN can communicate with them
LAN Segmentation
VLANs allow logical network topologies to overlay the physical switched infrastructure such that any arbitrary collection of LAN ports can be combined into an autonomous user group or community of interest. The technology logically segments the network into separate Layer 2 broadcast domains whereby packets are switched between ports designated to be within the same VLAN. By containing traffic originating on a particular LAN only to other LANs in the same VLAN, switched virtual networks avoid wasting bandwidth.


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