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642-813 Q&A – Implement VLAN based solution (36-40)

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

Which of the following specification will allow you to: associate VLAN groups to STP instances so you can provide multiple forwarding paths for data traffic and enable load balancing?
A. IEEE 802.1d (STP)
B. IEEE 802.1s (MST)
C. IEEE 802.1Q (CST)
D. IEEE 802.1w (RSTP)

Answer: B
IEEE 802.1s MST Overview
MST extends the IEEE 802.1w rapid spanning tree (RST) algorithm to multiple spanning trees.
This extension provides both rapid convergence and load balancing in a VLAN environment. MST converges faster than PVST+. MST is backward compatible with 802.1D STP, 802.1w (rapid spanning tree protocol [RSTP]), and the Cisco PVST+ architecture.

The Company LAN is becoming saturated with broadcasts and multicast traffic. What could you do to help a network with many multicasts and broadcasts?
A. Creating smaller broadcast domains by implementing VLANs.
B. Separate nodes into different hubs.
C. Creating larger broadcast domains by implementing VLANs.
D. Separate nodes into different switches.
E. All of the above.
Answer: A
Controlling broadcast propagation throughout the network is important to reduce the amount of overhead associated with these frames. Routers, which operate at Layer 3 of the OSI model, provide broadcast domain segmentation for each interface. Switches can also provide broadcast domain segmentation using virtual LANs (VLANs). A VLAN is a group of switch ports, within a single or multiple switches, that is defined by the switch hardware and/or software as a single broadcast domain. A VLANs goal is to group devices connected to a switch into logical broadcast domains to control the effect that broadcasts have on other connected devices. A VLAN can be characterized as a logical network.

The Company network utilizes the Multiple-instance Spanning Tree protocol in its switched LAN.
Which three statements about the MST protocol (IEEE 802.1S) are true? (Select three)
A. To verify the MST configuration, the show pending command can be used in MST configuration mode.
B. When RSTP and MSTP are configured; UplinkFast and BackboneFast must also be enabled.
C. All switches in the same MST region must have the same VLAN-to-instance mapping, but different configuration revision numbers.
D. All switches in an MST region, except distribution layer switches, should have their priority lowered from the default value 32768.
E. An MST region is a group of MST switches that appear as a single virtual bridge to adjacent CST and MST regions.
F. Enabling MST with the "spanning-tree modemst" global configuration command also enables RSTP.
Answer: A,E,F
MST is built on the concept of mapping one or more VLANs to a single STP instance. Multiple instances of STP can be used (hence the name MST), with each instance supporting a different group of VLANs.
Each could be tuned to result in a different topology, so that Instance 1 would forward on the left uplink, while Instance 2 would forward on the right uplink. Therefore, VLAN A would be mapped to Instance 1, and VLAN B to Instance 2.
To implement MST in a network, you need to determine the following: The number of STP instances needed to support the desired topologies. Whether to map a set of VLANs to each instance.

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
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

Refer to the exhibit. On the basis of the output generated by the show commands, which two statements are true? (Choose two.)

A. Because it is configured as a trunk interface, interface gigabitethernet 0/1 does not appear in the show vlan output.
B. VLAN 1 will not be encapsulated with an 802.1q header.
C. There are no native VLANs configured on the trunk.
D. VLAN 2 will not be encapsulated with an 802.1q header.
E. All interfaces on the switch have been configured as access ports.
F. Because it has not been assigned to any VLAN, interface gigabitethernet 0/1 does not appear in the show vlan output.
Answer: A,B
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. show vlan: This commands shows the vlan, ports belonging to VLAN means that port on access mode. It doesn’t show the port on trunk mode.

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One thought on “642-813 Q&A – Implement VLAN based solution (36-40)

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