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642-813 Q&A – Implement VLAN based solution (21-25)

Section 1 – Implement VLAN based solution, given a network design and a set of requirements

You need make configuration changes to an existing layer 3 switch in the Company network. On a multilayer Catalyst switch, which interface command is used to convert a Layer 3 interface to a Layer 2 interface?
A. switchport access vlan vlan-id
B. switchport
C. switchport mode access
D. no switchport
E. None of the other alternatives apply

Answer: B
The switchport command puts the port in Layer 2 mode. Then, you can use other switchport command keywords to configure trunking, access VLANs, and so on.

The core Company switches are configured to use 802.1Q trunks. Which three statements are correct with regard to the IEEE 802.1Q standard? (Select three)
A. The IEEE 802.1Q frame format adds a 4 byte field to a Ethernet frame
B. The packet is encapsulated with a 26 byte header and a 4 byte FCS
C. The protocol uses point-to-multipoint connectivity
D. The protocol uses point-to-point connectivity
E. The IEEE 802.1Q frame uses multicast destination of 0x01-00-0c-00-00
F. The IEEE 802.1Q frame retains the original MAC destination address
Answer: A,D,F
The IEEE 802.1Q protocol can also carry VLAN associations over trunk links. However, this frame identification method is standardized, allowing VLAN trunks to exist and operate between equipment from multiple vendors.
In particular, the IEEE 802.1Q standard defines an architecture for VLAN use, services provided with VLANs, and protocols and algorithms used to provide VLAN services. Like Cisco ISL, IEEE802.1Q can be used for VLAN identification with Ethernet trunks. Instead of encapsulating each frame with a VLAN ID header and trailer, 802.1Q embeds its tagging information within the Layer 2 frame. This method is referred to as single-tagging or internal tagging .
802.1Q also introduces the concept of a native VLAN on a trunk. Frames belonging to this VLAN are not encapsulated with any tagging information. In the event that an end station is connected to an 802.1Q trunk link, the end station can receive and understand only the native VLAN frames.
This provides a simple way to offer full trunk encapsulation to the devices that can understand it, while giving normal access stations some inherent connectivity over the trunk.

Switch R1 has been configured with the root guard feature. What statement is true if the spanning tree enhancement Root Guard is enabled?
A. If BPDUs are not received on a non-designated port, the port is moved into the STP loopinconsistent blocked state
B. IF BPDUs are received on a PortFast enabled port, the port is disabled.
C. If superior BPDUs are received on a designated port, the interface is placed into the rootinconsistent blocked state.
D. If inferior BPDUs are received on a root port, all blocked ports become alternate paths to the root bride.
Answer: C
Root guard is configured on a per-port basis, and does not allow the port to become a STP root port. This means that the port is always STP-designated. If there is a better BPDU received on this port, root guard will put the port into root-inconsistent STP state, rather than taking the BPDU into account and electing a new STP root. Root guard needs to be enabled on all ports where the root bridge should not appear. In a way one can configure a perimeter around part of network where STP root is allowed to be located.

Switch R1 is part of the Company VTP domain. What’s true of VTP Pruning within this domain?  (Select all that apply)
A. It does not prune traffic from VLANs that are pruning-ineligible
B. VLAN 1 is always pruning-eligible
C. it will prune traffic from VLANs that are pruning-ineligible
D. VLAN 2 is always pruning-ineligible
E. None of the other alternatives apply.
Answer: A
By definition, pruning-ineligible VLANs can not be pruned. You can make specific
VLANs pruning ineligible with the clear vtp pruneeligible vlan_range command. By default, VLANs 2-1000 are pruning-eligible. Since the default VLAN for any switch port in a Catalyst switch is VLAN 1, it is not eligible for pruning.
Incorrect Answers:
B: VLAN 1 is always pruning-ineligible
C: The opposite is true.
D: By default, VLANs 2-1000 are eligible to be pruned.

You’re a network administer and you issue the command (show port 3/1) on an Ethernet port. To your surprise you notice a non-zero entry in the ‘Giants’ column. What could be the cause of this?
A. IEEE 802.1Q
B. IEEE 802.10
C. Misconfigured NIC
D. User configuration
E. All of the above
Answer: A
The 802.1Q standard can create an interesting scenario on the network. Recalling that the maximum size for an Ethernet frame as specified by IEEE 802.3 is 1518 bytes, this means that if a maximum-sized Ethernet frame gets tagged, the frame size will be 1522 bytes, a number that violates the IEEE 802.3 standard. To resolve this issue, the 802.3 committee created a subgroup called 802.3ac to extend the maximum Ethernet size to 1522 bytes.
Note: The show port command is used to display port status and counters. Giants denote the number of received giant frames (frames that exceed the maximum IEEE 802.3 frame size) on the port.

One thought on “642-813 Q&A – Implement VLAN based solution (21-25)

  1. neo1674 says:

    On question 25, I believe all of the first 4 options are possible causes for a larger-than-usual frame to be received on a switch port. All of them could potentialy exceed the default MTU on the switch ports, therefore registering as a giant frame… the answer should be E, wouldn’t you agree?

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