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    CCNA 640-802 Bible – Basic Operations On Cisco Switch

    By admin | July 7, 2009

    1. Which two values are used by Spanning Tree Protocol to elect a root bridge? (Choose two.)

    A:amount of RAM

    B:bridge priority

    C:IOS version

    D:IP address

    E:MAC address

    F:speed of the links

    Correct Answers: B, E

    Explanation:

    Switch having lowest bridge ID will become the root bridge. The bridge ID is how keeps track of all the switches in the network. It is determined by a combination of the bridge priority (32,768 by default on all Cisco switches) and the base MAC address. The bridge with the lowest bridge ID becomes the root bridge in the network.

    2. What will an Ethernet switch do if it receives a unicast frame with a destination MAC that is listed in the switch table?

    A: The switch will not forward unicast frames.

    B: The switch will forward the frame to a specific port.

    C: The switch will return a copy of the frame out the source port.

    D: The switch will remove the destination MAC from the switch table.

    E: The switch will forward the frame to all ports except the port on which it was received.

    Correct Answers: B

    Explanation:

    How Does the Switch Find Host MACs?

    Let’s use the diagram below to help us understand how address learning process takes place.

    clip_image002

    Let’s assume that we have just powered on the switch. It has nothing in its MAC table. We connect the cables from the hosts on the switch interfaces as shown in the diagram. Host A initiates a connection towards Host D, and the following takes place:

    1. Host A (interface fe0/0) sends a frame to Host D (MAC address:0000.43c5.334c).

    2. The switch inspects the Source Address in the frame and notes in its table the MAC address of Host A along with the Interface number from which the frame originated.

    3. The switch inspects the Destination Address in the frame. If the destination MAC address is already in the MAC address table, direct communication to the host will happen at this point. If it does not have Hosts D MAC address in its table, it constructs a broadcast frame and forwards out all interfaces except the interface from where the original frame arrived.

    4. Host D identifies itself as the expected recipient and responds back to Host A. The switch receives the respond frame on interface fe0/11 and places the SA in its table along with the interface number where the frame came from.

    5. From now on, further communication between the two hosts will be switched to the appropriate interfaces based on the MAC tables entries.

    This process takes place every time a new host is attached on the switch and initiates traffic. The switch tries to keep its MAC table up-to-date, therefore if some hosts do not initiate traffic for a certain amount of time, the switch removes them from its table and reinserts them when they begin sending traffic.

    3. 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.

    Correct Answers: C

    Explanation:

    There are three different address types:

    * Unicast : One source to One destination

    * Broadcast: One source to multiple destination

    * Multicast: One source to multiple destination joined to group

    On unicast or broadcast or multicast communication, the source address is always the unicast address but the destination address can be unicast, broadcast or multicast.

    4. Drop

    clip_image004

    Drag and drop question. Drag the items to the proper locations.

    Correct Answers:

    clip_image006

    enable : This command is used to enter into User Privileges Mode

    configure terminal: This command is used to enter into global configuration mode

    hostname : This command is used to set the hostname of switch

    ip default-gateway : This command should enter should enter on global configuration mode to set default gateway of switch.

    Interface vlan 1 : Enters into the vlan 1 SVI (Switched Virtual Interface) configuration mode, where you can enter vlan 1 SVI interface specific configuration

    ip add x.x.x.x y.y.y.y : Use to assign the ip address on interface no shutdown: Brings the interface on up state from administratively down state

    5. Refer to the exhibit. Why does the switch have two MAC addresses assigned to the FastEthernet 0/1 port in the switch address table?

    clip_image007

    A: Data from two of the devices connected to the switch has been sent to Host3.

    B: Data from Host3 and Host4 has been received by switch port FastEthernet 0/1.

    C: Either Host3 or Host4 has just had the NIC replaced.

    D: Host3 and Host4 are on two different VLANs.

    Correct Answers: B

    Explanation:

    Switches learn the MAC addresses of PCs or workstations that are connected to their switch ports by examining the source address of frames that are received on that port.

    When more than one device is attached to a switch port, such as via the use of a hub as shown in this example, the switch will retain the MAC address of each of the known devices on that port.

    6. The system LED is amber on a Cisco Catalyst 2950 series switch. What does this indicate?

    A: The system is malfunctioning.

    B: The system is not powered up.

    C: The system is powered up and operational.

    D: The system is forwarding traffic.

    E: The system is sensing excessive collisions.

    Correct Answers: A

    Explanation:

    While the switch powers on, it begins POST, a series of tests. POST runs automatically to verify that the switch functions properly. When the switch begins POST, the system LED is off. If POST completes successfully, the LED turns green. If POST fails, the LED turns amber.

    Note: POST failures are usually fatal. Call Cisco Systems if your switch does not pass POST.


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    Topics: 640-802 Bible, CCNA, CCNA R&S | No Comments »

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