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642-813 Q&A – Implement VLAN based solution (61-65)

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

ISL is being configured on a Company switch. Which of the following choices are true regarding the ISL protocol? (Select two)
A. It can be used between Cisco and non-Cisco switch devices.
B. It calculates a new CRC field on top of the existing CRC field.
C. It adds 4 bytes of protocol-specific information to the original Ethernet frame.
D. It adds 30 bytes of protocol-specific information to the original Ethernet frame.

Answer: B,D
ISL adds a total of 30bytes to the Ethernet frame. A 26 byte header (10bytes identifies the VLAN ID) and a 4 byte trailer (containing a separate CRC).
Incorrect Answers:
A: This is incorrect because ISL is Cisco proprietary and can only be used on Cisco devices. For configuring a trunk to a non-Cisco switch, 802.1Q encapsulation should be used.
C: This is incorrect because it is contradictory to D. 30 byes are added with ISL, not 4 bytes. This choice describes what is used in 802.1Q frames, not ISL

The Company core switches use 802.1Q trunks to connect to each other. How does 802.1Q trunking keep track of multiple VLANs?
A. It tags the data frame with VLAN information and recalculates the CRC value
B. It encapsulates the data frame with a new header and frame check sequence
C. It modifies the port index of a data frame to indicate the VLAN
D. It adds a new header containing the VLAN ID to the data frame
E. None of the other alternatives apply
Answer: A
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, IEEE 802.1Q 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.

You need to connect two Company core switches via an ISL trunk. Which statement is true regarding the configuration of ISL trunks?
A. A Catalyst switch cannot have ISL and IEEE 802.1q trunks enabled.
B. All Catalyst switches support ISL trunking.
C. A Catalyst switch will report giants if one side is configured for ISL while the other side is not.
D. ISL trunking requires that native VLANs match.
E. None of the other alternatives apply
Answer: C
The Inter-Switch Link (ISL) protocol is a Cisco proprietary method for preserving the source VLAN identification of frames passing over a trunk link. ISL performs frame identification in Layer 2 by encapsulating each frame between a header and trailer. Any Cisco switch or router device configured for ISL can process and understand the ISL VLAN information. ISL is primarily used for Ethernet media, although Cisco has included provisions to carry Token Ring, FDDI, and ATM frames over Ethernet ISL. (A Frame-Type field in the ISL header indicates the source frame type.)
When a frame is destined out a trunk link to another switch or router, ISL adds a 26-byte header and a 4-byte trailer to the frame. The source VLAN is identified with a 10-bit VLAN ID field in the header. The trailer contains a cyclic redundancy check (CRC) value to ensure the data integrity of the new encapsulated frame. Figure 6-3 shows how Ethernet frames are encapsulated and forwarded out a trunk link. Because tagging information is added at the beginning and end of each frame, ISL is sometimes referred to as double tagging.

If you were to set up a VLAN trunk over a Fast Ethernet link on switch R1, which trunk mode would you set the local port to on R1 if you wanted it to respond to requests from its link partner (R2) and become a trunk?
A. Auto
B. Negotiate
C. Designate
D. No negotiate
Answer: A
Only ports in desirable and auto mode will negotiate a channel (either desirable-auto or desirable).
Ports in on mode will only form a functional channel with other ports in on mode (they will not negotiate a channel with ports in desirable or auto mode).

Static VLANs are being used on the Company network. What is true about static VLANs?
A. Devices use DHCP to request their VLAN.
B. Attached devices are unaware of any VLANs.
C. Devices are assigned to VLANs based on their MAC addresses.
D. Devices are in the same VLAN regardless of which port they attach to.
Answer: B
LAN port VLAN membership can be assigned manually on a port-by-port basis. When you assign
LAN ports to VLANs using this method, it is known as port-based, or static, VLAN membership.
Attached devices will be unaware of any VLANs.
Incorrect Answers:
A: The DHCP service is not involved in VLAN assignment.
C: Devices are not assigned to VLAN based on their MAC addresses. This is a function of dynamic VLANs.
D: Static VLANs are configured on a port by port basis.

2 thoughts on “642-813 Q&A – Implement VLAN based solution (61-65)

  1. mutsetse says:

    are these from real exams

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