Home » SWITCH 642-813 Q&As » Section 4 - Prepare Infrastructure » 642-813 Q&A – Prepare infrastructure to support advanced services (41-45)

642-813 Q&A – Prepare infrastructure to support advanced services (41-45)

Section4 – Prepare infrastructure to support advanced services

QUESTION NO: 41
Which two Lightweight Access Point Protocol (LWAPP) statements are true? (Choose two.)
A. Control traffic is encapsulated in UDP packets with a source port of 1024 and a destination port of 12223.
B. Control traffic is encapsulated in TCP packets with a source port of 1024 and a destination port of 12223.
C. Data traffic is encapsulated in UDP packets with a source port of 1024 and a destination port of 12223.
D. Data traffic is encapsulated in TCP packets with a source port of 1024 and destination port of 12223.
E. Layer 3 LWAPP is a UDP / IP frame that requires a Cisco Aironet AP to obtain an IP address using DHCP.
F. LWAPP is a proprietary protocol, and because of its very high overhead it is not widely adopted .
Answer: A E

Explanation:
For Layer 3, LWAPP uses packets in a UDP/IP frame. LWAPP control traffic uses source port 1024 or greater and destination port 12223, and LWAPP data traffic uses source port 1024 or greater and destination port 12222. The Cisco wireless LAN controller and access point can be connected to the same VLAN/subnet or to a different VLAN/subnet.
In Layer 3 operation, the access point and the controller can be on the same or different subnets.
Layer 3 operation is scalable and is recommended by Cisco. A Layer 3 access point on a different subnet than the controller requires a DHCP server on the access point subnet and a route to the controller. The route to the controller must have destination UDP ports 12222 and 12223 open for LWAPP communications. The route to the primary, secondary, and tertiary controllers must allow IP packet fragments.

QUESTION NO: 42
Which two statements are true about the operation of voice VLANs on a Catalyst switch? (Choose two.)
A. Enabling voice VLANs enables the switch to create multiple queues for traffic that is entering a port.
B. Enabling voice VLANs enables the switch to forward frames with a specific 802.1P marking.
C. Voice VLANs are configured to enable the switch to forward frames marked with the proper CoS values over separate physical links.
D. When voice VLANs are configured on a trunk link, UplinkFast must also be enabled.
E. When the voice VLAN feature is enabled, all untagged traffic is sent according to the default CoS priority of the port.
Answer: BE

QUESTION NO: 43
Which two statements are true about voice packets in a LAN? (Select two)
A. Voice traffic data flow involves large volumes of large packets.
B. Because a packet loss involves a small amount of data, voice traffic is less affected by packet losses than traditional data traffic is.
C. Voice carrier stream utilizes Real-Time Transport Protocol (RTP) to carry the audio/media portion of the VoIP communication.
D. Voice packets are very sensitive to delay and jitter.
E. Voice packets are encapsulated in TCP segments to allow for proper sequencing during delivery.
Answer: C,D
Explanation:
Two major factors affect voice quality: lost packets and delayed packets. Packet loss causes voice clipping and skips. Packet delay can cause either voice quality degradation, due to the end-to-end voice latency, or packet loss, if the delay is variable. If the end-to-end voice latency becomes too long (250 Msec, for example), the conversation begins to sound like two parties talking on a CB radio. If the delay is variable, there is a risk of jitter buffer overruns at the receiving end.

QUESTION NO: 44
Which statement describes the function of a trust boundary?
A. Trust boundaries determine whether certain types of traffic can pass.
B. Trust boundaries are a point in the network where decisions about CoS markings on incoming packets are made.
C. Trust boundaries are a point in the network where QoS functionality begins and ends.
D. Trust boundaries are points in the network where Layer 2 CoS markings are converted to Layer 3 DSCP or IP precedence markings.
Answer: B
Explanation:
The perimeter formed by switches that do not trust incoming QoS is called the trust boundary.
Usually, the trust boundary exists at the farthest reaches of the enterprise network (access-layer switches and WAN or ISP demarcation points). When the trust boundary has been identified and the switches there are configured with untrusted ports, everything else inside the perimeter can be configured to blindly trust incoming QoS values since the COS/QOS markings are then under the control of the network administrator, and not the end user.

QUESTION NO: 45
Refer to the exhibit. Based upon the information that is given, how will voice traffic from the phone and data traffic from the PC be handled by SW_1?

45
A.The switch port will trust the CoS value of the ingress voice and data traffic that comes into the switch port.
B.The switch port will perform marking for the ingress voice and data traffic by using the default CoS value at the switch port.
C.The switch port will trust the CoS value of the ingress voice traffic. Data traffic will be marked at the switch port with the default CoS value.
D.The switch port will trust the CoS value of the ingress data traffic. Voice traffic will be marked at the switch port with the default CoS value.
Answer: A
Explanation:
In a typical network, you connect a Cisco IP Phone to a switch port. Traffic sent from the telephone to the switch is typically marked with a tag that uses the 802.1Q header. The header contains the VLAN information and the CoS 3-bit field, which determines the priority of the packet.
For most Cisco IP Phone configurations, the traffic sent from the telephone to the switch is trusted to ensure that voice traffic is properly prioritized over other types of traffic in the network. By using the mls qos trust cos interface configuration command, you can configure the switch port to which the telephone is connected to trust the CoS labels of all traffic received on that port.

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