CISCO CCNA Exam – Q28

Refer to Exhibit:
CISCO CCNA Exam – Q28

How many broadcast domains are shown in the graphic assuming only the default VLAN is configured on the switches?

A. one
B. two
C. six
D. twelve

Correct Answer: A

Explanation:
Only router can break up broadcast domains but in this exhibit no router is used so there is only 1 broadcast domain.
For your information, there are 7 collision domains in this exhibit (6 collision domains between hubs & switches + 1 collision between the two switches).

CISCO CCNA Exam – Q27

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.

Correct Answers: A, C, E

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.

CISCO CCNA Exam – Q26

Refer to the exhibit.
CISCO CCNA Exam – Q26
The output that is shown is generated at a switch. Which three statements are true? (Choose three.)

A. All ports will be in a state of discarding, learning, or forwarding.
B. Thirty VLANs have been configured on this switch.
C. The bridge priority is lower than the default value for spanning tree.
D. All interfaces that are shown are on shared media.
E. All designated ports are in a forwarding state.
F. This switch must be the root bridge for all VLANs on this switch.

Correct Answer: A, C, E

Explanation:
From the output, we see that all ports are in designated role (forwarding state).
The command “show spanning-tree vlan 30″ only shows us information about VLAN 30. We don’t know how many VLAN exists in this switch.
The bridge priority of this switch is 24606 which is lower than the default value bridge priority 32768.
All three interfaces on this switch have the connection type “p2p”, which means Point-to-point environment – not a shared media.
The only thing we can specify is this switch is the root bridge for VLAN 3o but we cannot guarantee it is also the root bridge for other VLANs.

CISCO CCNA Exam – Q25

Refer to the exhibit.
CISCO CCNA Exam – Q25

At the end of an RSTP election process, which access layer switch port will assume the discarding role?

A. Switch3, port fa0/1
B. Switch3, port fa0/12
C. Switch4, port fa0/11
D. Switch4, port fa0/2
E. Switch3, port Gi0/1
F. Switch3, port Gi0/2

Correct Answer: C

Explanation:
In this question, we only care about the Access Layer switches (Switch3 & 4). Switch 3 has a lower bridge ID than Switch 4 (because the MAC of Switch3 is smaller than that of Switch4) so both ports of Switch3 will be in forwarding state. The alternative port will surely belong to Switch4.
Switch4 will need to block one of its ports to avoid a bridging loop between the two switches. But how does Switch4 select its blocked port? Well, the answer is based on the BPDUs it receives from Switch3. A BPDU is superior to another if it has:

1. A lower Root Bridge ID
2. A lower path cost to the Root
3. A lower Sending Bridge ID
4. A lower Sending Port ID

These four parameters are examined in order. In this specific case, all the BPDUs sent by Switch3 have the same Root Bridge ID, the same path cost to the Root and the same Sending Bridge ID. The only parameter left to select the best one is the Sending Port ID (Port ID = port priority + port index). In this case the port priorities are equal because they use the default value, so Switch4 will compare port index values, which are unique to each port on the switch, and because Fa0/12 is inferior to Fa0/1, Switch4 will select the port connected with Fa0/1 (of Switch3) as its root port and block the other port -> Port fa0/11 of Switch4 will be blocked (discarding role).

CISCO CCNA Exam – Q24

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

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

Correct Answer: A. converged

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.

CISCO CCNA Exam – Q23

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

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

Correct Answer: B, C, D
Section: LAN Switching Technologies

Explanation:
These are the different types of trunk modes:

ON: This mode puts the port into permanent trunk mode and negotiates to convert the link into a trunk link. The port becomes a trunk port even if the adjacent port does not agree to the change.
OFF: This mode puts the port into permanent non-trunk mode and negotiates to convert the link into a non-trunk link. The port becomes a non-trunk port even if the adjacent port does not agree to the change.
Desirable: This mode causes the port to actively attempt to convert the link into a trunk link. The port becomes a trunk port if the adjacent port is set to on, desirable, or auto mode.
Auto: This mode enables the port to convert the link into a trunk link. The port becomes a trunk port if the adjacent port is set to on or desirable mode. This is the default mode for Fast and Gigabit Ethernet ports.
Nonegotiate: This mode puts the port into permanent trunk mode, but does not allow the port to generate Dynamic Trunking Protocol (DTP) frames. The adjacent port must be configured manually as a trunk port to establish a trunk link.

CISCO CCNA Exam – Q22

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.

Correct Answers: B, E

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.

CISCO CCNA Exam – Q21

Refer to the exhibit.

CISCO CCNA Exam – Q21

Which two statements are true of the interfaces on Switch1? (Choose two.)

A. Multiple devices are connected directly to FastEthernet0/1.
B. A hub is connected directly to FastEthernet0/5.
C. FastEthernet0/1 is connected to a host with multiple network interface cards.
D. FastEthernet0/5 has statically assigned MAC addresses.
E. FastEthernet0/1 is configured as a trunk link.
F. Interface FastEthernet0/2 has been disabled.

Correct Answers: B, E

Explanation:
Carefully observe the information given after command show. Fa0/1 is connected to Switch2, seven MAC addresses correspond to Fa0/1, and these MAC are in different VLAN. From this we know that Fa0/1 is the trunk interface.
From the information given by show cdp neighbors we find that there is no Fa0/5 in CDP neighbor. However, F0/5 corresponds to two MAC addresses in the same VLAN. Thus we know that Fa0/5 is connected to a Hub.
Based on the output shown, there are multiple MAC addresses from different VLANs attached to the FastEthernet 0/1 interface. Only trunks are able to pass information from devices in multiple VLANs.

CISCO CCNA Exam – Q20

Three switches are connected to one another via trunk ports. Assuming the default switch configuration, which switch is elected as the root bridge for the spanning-tree instance of VLAN 1?

A. the switch with the highest MAC address
B. the switch with the lowest MAC address
C. the switch with the highest IP address
D. the switch with the lowest IP address

Correct Answer: B

Explanation:
Each switch in your network will have a Bridge ID Priority value, more commonly referred to as a BID. This BID is a combination of a default priority value and the switch’s MAC address, with the priority value listed first. The lowest BID will win the election process.

For example, if a Cisco switch has the default priority value of 32,768 and a MAC address of 11-22-33-44-55-66, the BID would be 32768:11-22-33-44-55-66. Therefore, if the switch priority is left at the default, the MAC address is the deciding factor in the root bridge election.

CISCO CCNA Exam – Q19

What are three advantages of VLANs? (Choose three.)

A. VLANs establish broadcast domains in switched networks.
B. VLANs utilize packet filtering to enhance network security.
C. VLANs provide a method of conserving IP addresses in large networks.
D. VLANs provide a low-latency internetworking alternative to routed networks.
E. VLANs allow access to network services based on department, not physical location.
F. VLANs can greatly simplify adding, moving, or changing hosts on the network.

Correct Answers: A, E, F
Explanation:
VLAN technology is often used in practice, because it can better control layer2 broadcast to improve network security. This makes network more flexible and scalable.
Packet filtering is a function of firewall instead of VLAN.