Free 2014 Latest Cisco 200-120 Dump (21-30) Download!

QUESTION 21
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.

QUESTION 22
Which command can be used from a PC to verify the connectivity between hosts that connect through a switch in the same LAN?

A.    pingaddress
B.    tracertaddress
C.    tracerouteaddress
D.    arpaddress

Answer: A
Explanation:
ICMP pings are used to verify connectivity between two IP hosts. Traceroute is used to verify the router hop path traffic will take but in this case since the hosts are in the same LAN there will be no router hops involved.

QUESTION 23
Which two of these are characteristics of the 802.1Q protocol? (Choose two.)

A.    It is used exclusively for tagging VLAN frames and does not address network reconvergence following
switched network topology changes.
B.    It modifies the 802.3 frame header, and thus requires that the FCS be recomputed.
C.    It is a Layer 2 messaging protocol which maintains VLAN configurations across networks.
D.    It includes an 8-bit field which specifies the priority of a frame.
E.    It is a trunking protocol capable of carrying untagged frames.

Answer: BE
Explanation:
802.1Q protocol, or Virtual Bridged Local Area Networks protocol, mainly stipulates the realization of the VLAN. 802.1Q is a standardized relay method that inserts 4 bytes field into the original Ethernet frame and re-calculate the FCS. 802.1Q frame relay supports two types of frame: marked and non-marked. Non-marked frame carries no VLAN identification information.

QUESTION 24
Refer to the exhibit. Each of these four switches has been configured with a hostname, as well as being configured to run RSTP. No other configuration changes have been made. Which three of these show the correct RSTP port roles for the indicated switches and interfaces? (Choose three.)

A.    SwitchA, Fa0/2, designated
B.    SwitchA, Fa0/1, root
C.    SwitchB, Gi0/2, root
D.    SwitchB, Gi0/1, designated
E.    SwitchC, Fa0/2, root
F.    SwitchD, Gi0/2, root

Answer: ABF
Explanation:
The question says “no other configuration changes have been made” so we can understand these switches have the same bridge priority. Switch C has lowest MAC address so it will become root bridge and 2 of its ports (Fa0/1 & Fa0/2) will be designated ports. Because SwitchC is the root bridge so the 2 ports nearest SwitchC on SwitchA (Fa0/1) and SwitchD (Gi0/2) will be root ports..
Now we come to the most difficult part of this question: SwitchB must have a root port so which port will it choose? To answer this question we need to know about STP cost and port cost. In general, “cost” is calculated based on bandwidth of the link. The higher the bandwidth on a link, the lower the value of its cost. Below are the cost values you should memorize:

SwitchB will choose the interface with lower cost to the root bridge as the root port so we must calculate the cost on interface Gi0/1 & Gi0/2 of SwitchB to the root bridge. This can be calculated from the “cost to the root bridge” of each switch because a switch always advertises its cost to the root bridge in its BPDU. The receiving switch will add its local port cost value to the cost in the BPDU.
One more thing to notice is that a root bridge always advertises the cost to the root bridge (itself) with an initial value of 0.
Now let’s have a look at the topology again

SwitchC advertises its cost to the root bridge with a value of 0. Switch D adds 4 (the cost value of 1Gbps link) and advertises this value (4) to SwitchB. SwitchB adds another 4 and learns that it can reach SwitchC via Gi0/1 port with a total cost of 8. The same process happens for SwitchA and SwitchB learns that it can reach SwitchC via Gi0/2 with a total cost of 23 -> Switch B chooses Gi0/1 as its root port ->
Now our last task is to identify the port roles of the ports between SwitchA & SwitchB. It is rather easy as the MAC address of SwitchA is lower than that of SwitchB so Fa0/2 of SwitchA will be designated port while Gi0/2 of SwitchB will be alternative port.
Below summaries all the port roles of these switches:

+ DP: Designated Port (forwarding state)
+ RP: Root Port (forwarding state)

QUESTION 25
What is one benefit of PVST+?

A.    PVST+ supports Layer 3 load balancing without loops.
B.    PVST+ reduces the CPU cycles for all the switches in the network.
C.    PVST+ allows the root switch location to be optimized per VLAN.
D.    PVST+ automatically selects the root bridge location, to provide optimized bandwidth usage.

Answer: C
Explanation:
The PVST+ provides Layer 2 load-balancing for the VLAN on which it runs. You can create different logical topologies by using the VLANs on your network to ensure that all of your links are used but that no one link is oversubscribed. Each instance of PVST+ on a VLAN has a single root switch. This root switch propagates the spanning-tree information associated with that VLAN to all other switches in the network. Because each switch has the same information about the network, this process ensures that the network topology is maintained and optimized per VLAN.
Reference:
http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_55_se /configuration/guide/swstp.html

QUESTION 26
Which are valid modes for a switch port used as a VLAN trunk? (Choose three.)

A.    transparent
B.    auto
C.    on
D.    desirable
E.    blocking
F.    forwarding

Answer: BCD

QUESTION 27
Which three of these statements regarding 802.1Q trunking are correct? (Choose three.)

A.    802.1Q native VLAN frames are untagged by default.
B.    802.1Q trunking ports can also be secure ports.
C.    802.1Q trunks can use 10 Mb/s Ethernet interfaces.
D.    802.1Q trunks require full-duplex, point-to-point connectivity.
E.    802.1Q trunks should have native VLANs that are the same at both ends.

Answer: ACE
Explanation:
By default, 802.1Q trunk defined Native VLAN in order to forward unmarked frame. Switches can forward Layer 2 frame from Native VLAN on unmarked trunks port. Receiver switches will transmit all unmarked packets to Native VLAN. Native VLAN is the default VLAN configuration of port. Note for the 802.1Q trunk ports between two devices, the same Native VLAN configuration is required on both sides of the link. If the Native VLAN in 802.1Q trunk ports on same trunk link is properly configured, it could lead to layer 2 loops. The 802.1Q trunk link transmits VLAN information through Ethernet.

QUESTION 28
Which term describes a spanning-tree network that has all switch ports in either the blocking or fowarding state?

A.    converged
B.    redundant
C.    provisioned
D.    spanned

Answer: A
Explanation:
Spanning Tree Protocol convergence (Layer 2 convergence) happens when bridges and switches have transitioned to either the forwarding or blocking state. When layer 2 is converged, root bridge is elected and all port roles (Root, Designated and Non-Designated) in all switches are selected.

QUESTION 29
What are the possible trunking modes for a switch port? (Choose three.)

A.    transparent
B.    auto
C.    on
D.    desirable
E.    client
F.    forwarding

Answer: BCD

QUESTION 30
Which two of these statements regarding RSTP are correct? (Choose two.)

A.    RSTP cannot operate with PVST+.
B.    RSTP defines new port roles.
C.    RSTP defines no new port states.
D.    RSTP is a proprietary implementation of IEEE 802.1D STP.
E.    RSTP is compatible with the original IEEE 802.1D STP.

Answer: BE
Explanation:
When network topology changes, rapid spanning tree protocol (IEEE802.1W, referred to as RSTP) will speed up significantly the speed to re-calculate spanning tree. RSTP not only defines the role of other ports: alternative port and backup port, but also defines status of 3 ports: discarding status, learning status, forwarding status.
RSTP is 802.1D standard evolution, not revolution. It retains most of the parameters, and makes no changes.

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