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What happens when an untagged frame is received on a Cisco switch trunk port?
A) The frame is forwarded to the default native VLAN
B) The frame is dropped
C) The switch assigns a VLAN to the untagged frame
D) The switch removes the VLAN tag from the frame
The correct answer is
A) The frame is forwarded to the default native VLAN.
When a switch trunk port receives an untagged frame, it is forwarded to the native VLAN. By default, the native VLAN is VLAN 1, but it is a best practice to change the native VLAN to a different VLAN. If there are no devices associated with the native VLAN, and there are no other trunk ports, the untagged frame will be dropped. However, receiving untagged frames on a trunk port is unusual in a well-designed network because all traffic should be tagged with the appropriate VLAN ID.
What is the purpose of the switchport mode access command when assigning a port to a VLAN?
A) To configure the port to negotiate with other switches to become a trunk link
B) To enable multiple VLANs on the port
C) To change the port to access mode and assign it to a single VLAN
D) To disable the port from being assigned to any VLAN
Answer: C) To change the port to access mode and assign it to a single VLAN
Explanation: When a port is assigned to a VLAN, it can be in either access mode or trunk mode. Access mode indicates that the port belongs to a single VLAN and will not negotiate to become a trunk link. Trunk mode, on the other hand, indicates that the port can carry traffic for multiple VLANs. The switchport mode access command is used to configure the port in access mode, and assign it to a single VLAN. This is a recommended security best practice, as it prevents unauthorized traffic from entering or leaving the VLAN on the port.
What does the show vlan summary command display?
A) A list of all configured VLANs.
B) The count of all configured VLANs.
C) A brief summary of all VLAN configurations.
D) VLAN information for a specific VLAN ID or name.
Answer: B) The count of all configured VLANs.
Explanation: The show vlan summary command displays a summary of all VLANs configured on the switch, including the total number of VLANs. It is a useful command to quickly check the number of VLANs configured on a switch without having to list them all individually.
What is the default PVID value for an 802.1Q trunk port if the native VLAN has not been reconfigured?
a) VLAN 99
b) VLAN 1
c) VLAN 100
d) There is no default PVID value.
Correct answer: b) VLAN 1
When we want to configure a trunk port to send traffic to multiple VLANs, we use a protocol called 802.1Q. This protocol adds a tag to each Ethernet frame, which identifies which VLAN the frame belongs to.
When an Ethernet frame comes into a trunk port and it does not have any tag, the switch needs to decide which VLAN the frame belongs to. For this, a Port VLAN ID (PVID) value is used. The PVID is assigned to each trunk port and it identifies the default VLAN for untagged frames that come into the port.
For example, if VLAN 99 is configured as the native VLAN and assigned as the PVID value for a trunk port, then any untagged frame that comes into that port is assigned to VLAN 99. Similarly, if the native VLAN has not been reconfigured, the PVID value is set to VLAN 1, and any untagged frames coming into the trunk port will be assigned to VLAN 1.
It is important to note that we should not have any untagged frames in a well-designed network. All devices should be configured to add tags to their frames, which will allow the switch to forward them to the correct VLANs.
How many VLANs can an access port be associated with?
A) Only one data VLAN at a time
B) Only one voice VLAN at a time
C) Both a data VLAN and a voice VLAN at the same time
D) Multiple data VLANs at the same time
Answer: A) Only one data VLAN at a time
Explanation: An access port can only belong to one data VLAN at a time. However, it can also be associated with a voice VLAN. This is useful when connecting an IP phone and an end device to the same port, as it allows the port to support both voice and data traffic.
What commands can be used to verify VLAN assignments on a specific interface of a Cisco switch?
A) show vlan summary
B) show interfaces fa0/18 summary
C) show interfaces interface-id switchport
D) show vlan
Answer: C) show interfaces interface-id switchport
Explanation: The command "show interfaces interface-id switchport" is used to display detailed information about the switchport configuration, including the VLAN assignments. This command is useful for verifying that an interface has been correctly assigned to a specific VLAN, or for troubleshooting VLAN-related issues on a specific interface. The other options are not relevant to verifying VLAN assignments on a specific interface.
How does a separate voice VLAN support VoIP?
A) It enables QoS and security policies to be applied to voice traffic.
B) It provides more bandwidth for voice traffic.
C) It allows voice traffic to be transmitted without any tagging.
D) It isolates voice traffic from data traffic.
Answer: A) It enables QoS and security policies to be applied to voice traffic.
When using VoIP (Voice over IP) technology, a separate voice VLAN is often necessary to provide better quality of service (QoS) and security policies. This is because voice traffic requires a high level of priority and reliability to ensure clear and uninterrupted calls. By creating a separate VLAN for voice traffic, network administrators can prioritize the traffic and apply QoS policies to ensure that it gets the bandwidth and latency it needs.
Voice VLAN tagging is a technique used to distinguish voice traffic from data traffic on a network. It involves assigning a specific VLAN to voice traffic so that it can be easily identified and managed by network devices. This is usually done using a 802.1Q tagging protocol that adds a special tag to the Ethernet frame header to indicate the VLAN membership of the frame.
Overall, using a separate VLAN for voice traffic is an important aspect of network design for organizations that use VoIP technology. It can help improve the quality of voice calls and ensure the security of voice traffic on the network.
What command is used to assign a voice VLAN to a port in a Cisco switch?
A) switchport mode access
B) switchport access vlan vlan-id
C) switchport trunk native vlan vlan-id
D) switchport voice vlan vlan-id
Answer: D) switchport voice vlan vlan-id
Explanation: To assign a voice VLAN to a port on a Cisco switch, the command "switchport voice vlan vlan-id" is used. This command is used in addition to assigning the port to a data VLAN with the "switchport access vlan vlan-id" command. The voice VLAN allows for voice traffic to be tagged with a separate VLAN ID and receive priority over other traffic on the network. This can help ensure that voice calls are of high quality and not affected by other network traffic.
What is the correct command to change a switch access port's VLAN membership if it has been assigned to the wrong VLAN?
A) switchport vlan 20
B) switchport access vlan 1
C) switchport access vlan 20
D) switchport trunk vlan 20
Answer: C) switchport access vlan 20.
Explanation: If a switch access port has been incorrectly assigned to a VLAN, it can be easily corrected by re-entering the switchport access vlan command with the correct VLAN ID. For example, if Fa0/18 was accidentally assigned to VLAN 1 instead of VLAN 20, the correct command to change it to VLAN 20 would be switchport access vlan 20. This will remove the port from the original VLAN and assign it to the new VLAN.
Where are the configuration details for normal range VLANs stored on a switch?
A) RAM memory
B) Hard drive
C) Flash memory
D) Virtual memory
Correct Answer: C) Flash memory
Explanation: When you create normal range VLANs on a switch, the configuration details are stored in a file called vlan.dat, which is saved in the flash memory of the switch. Flash memory is a type of non-volatile memory that can retain data even when the switch is powered off. Unlike RAM memory, which is volatile and loses its data when the switch is powered off, flash memory is persistent and does not require the copy running-config startup-config command. Therefore, you can save your VLAN configurations in flash memory and they will remain there even after the switch is rebooted. This makes flash memory a convenient place to store important switch configuration files, such as VLAN configurations.
What command is used to set the trusted state of an interface and to indicate which fields of the packet are used to classify traffic for enabling QoS in a LAN supporting voice traffic?
A) switchport voice vlan vlan-id
B) mls qos trust [cos | device cisco-phone | dscp | ip-precedence]
C) switchport mode access
D) vlan database
Answer: B) mls qos trust [cos | device cisco-phone | dscp | ip-precedence]
Explanation: Quality of service (QoS) is critical for LANs that support voice traffic to ensure that voice traffic is prioritized and delivered in a timely manner. Voice traffic must be labeled as trusted as soon as it enters the network to avoid any unnecessary delay or disruption. The mls qos trust command is used to set the trusted state of an interface, and it also indicates which fields of the packet are used to classify traffic. This command allows the network administrator to configure the switch to trust either the CoS value, DSCP value, IP precedence, or the Cisco IP phone device to classify the traffic.
What command is used to remove a VLAN from the switch vlan.dat file?
A) remove vlan vlan-id
B) delete vlan vlan-id
C) no vlan vlan-id
D) erase vlan vlan-id
C) no vlan vlan-id
Explanation:
To remove a VLAN from the switch vlan.dat file, the "no vlan vlan-id" command is used in the global configuration mode. This command deletes the VLAN from the VLAN database on the switch and removes any ports that are associated with it. It is important to note that this command should be used with caution, as removing a VLAN can have unintended consequences on the network.
Why is it good practice to save running configuration changes to the startup configuration when configuring VLANs on a Cisco switch?
A) To keep track of changes made to the VLAN configuration over time
B) To ensure that the VLAN configuration is retained after a reboot
C) To improve the performance of the switch's VLAN functionality
D) To reduce the likelihood of VLAN configuration errors
Answer: B) To ensure that the VLAN configuration is retained after a reboot.
Explanation: Saving the running configuration changes to the startup configuration ensures that the VLAN configuration is retained even after a switch reboot. If the changes are not saved, the switch will revert back to its previous configuration and any changes made will be lost. This is important for VLAN configurations because VLANs are often critical to the network topology and any loss of VLAN configuration could disrupt network traffic. Additionally, by keeping track of changes made over time, network administrators can troubleshoot issues that may arise and quickly identify when and where changes were made.
Which Cisco IOS command displays a list of all configured VLANs?
A) show vlan brief
B) show vlan id vlan-id
C) show vlan name vlan-name
D) show vlan summary
Answer: A) show vlan brief
Explanation: The "show vlan brief" command displays a list of all configured VLANs. This command can also be used with options such as "id vlan-id", "name vlan-name", or "summary" to filter the output. Using these options can provide additional information such as the VLAN ID or VLAN name. This command is useful for verifying that VLANs have been correctly configured on a Cisco switch.
What should be done before deleting a VLAN?
A) Nothing, you can delete the VLAN directly.
B) Reassign all member ports to another VLAN.
C) Disconnect all devices connected to the VLAN.
Answer: B) Reassign all member ports to another VLAN.
Explanation: Before deleting a VLAN, it is important to make sure that all member ports have been reassigned to a different VLAN. If any ports are not moved to an active VLAN, those ports will be unable to communicate with other hosts after the VLAN is deleted. This can result in network connectivity issues, so it is best to avoid this situation by reassigning ports before deleting a VLAN.