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

QUESTION NO: 41
While using a packet analyzer, you notice four additional bytes being added to the packets in the Company network. Which protocol inserts a four byte tag into the Ethernet frame and recalculates CRC value?
A. DTP
B. VTP
C. 802.1Q
D. ISL
E. None of the other alternatives apply
Answer: C

Explanation:
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.

QUESTION NO: 42
You need to configure a new Company switch to support DTP. Which DTP switchport mode parameter sets the switch port to actively send and respond to DTP negotiation frames?
A. Access
B. No negotiate
C. Trunk
D. Dynamic desirable
E. Dynamic auto
F. None of the other alternatives apply
Answer: D
Explanation: dynamic desirable (the default)—The port actively attempts to convert the link into trunking mode. If the far-end switch port is configured to trunk, dynamic desirable, or dynamic auto mode, trunking is successfully negotiated.

QUESTION NO: 43
A new Company switch was just configured using the “switchport trunk native vlan 7” command. What does this interface command accomplish?
A. Causes the interface to apply ISL framing for traffic on VLAN 7
B. Configures the trunking interface to forward traffic from VLAN 7
C. Configures the interface to be a trunking port and causes traffic on VLAN 7 to be 802.1q tagged
D. Configures the trunking interface to send traffic from VLAN 7 untagged
E. None of the other alternatives apply
Answer: D
Explanation:
In 802.1Q trunking, all VLAN packets are tagged on the trunk link to indicate the VLAN to which they belong. Frames belonging to the Native VLAN are sent untagged on the trunk link. The Native VLAN contains ports not assigned to other VLANs that by default belong to VLAN 1. VLAN 1 is the Native VLAN by default, but VLANs other than VLAN 1 may be designated as the Native VLAN. However, the Native VLAN must be the same on trunked switches in 802.1Q trunking. If a VLAN other than VLAN 1 is to be the Native VLAN, it needs to be identified on the trunk ports. In the interface configuration mode of the trunk port(s), the IOS-based command to designate the Native
VLAN is switchport trunk native. Switch(config-if)#switchport trunk native vlan vlan-id

QUESTION NO: 44
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
Explanation:
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.

QUESTION NO: 45
Refer to the exhibit. VLAN 1 and VLAN 2 are configured on the trunked links between Switch A and Switch B. Port Fa 0/2 on Switch B is currently in a blocking state for both VLANs. What should be done to load balance VLAN traffic between Switch A and Switch B?
A. Lower the port priority for VLAN 1 on port 0/1 for Switch A.
B. Lower the port priority for VLAN 1 on port 0/2 for Switch A.
C. Make the bridge ID of Switch B lower than the ID of Switch A.
D. Enable HSRP on the access ports.
Answer: B
Explanation: Load Sharing Using STP Port Priorities
When two ports on the same switch form a loop, the STP port priority setting determines which port is enabled and which port is in a blocking state. The priorities on a parallel trunk port can be set so that the port carries all the traffic for a given VLAN. The trunk port with the higher priority (lower values) for a VLAN is forwarding traffic for that VLAN. The trunk port with the lower priority (higher values) for the same VLAN remains in a Blocking state for that VLAN. One trunk port sends or receives all traffic for the VLAN.

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