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642-813 Q&A – Prepare infrastructure to support advanced services (26-30)

Section4 – Prepare infrastructure to support advanced services

Refer to the exhibit. Which two statements are true about the required switch configurations to support a voice VLAN? (Choose two.)


A.CDP must be disabled on the switch port to prevent interference between CDP messages and voice traffic.
B.CDP must be enabled on the switch port to allow configuration information to be passed to the IP phone.
C.Static secure MAC addresses should be configured on voice vlan ports to prevent access by devices other than IP phones.
D.Portfast must be enabled on the switch port.
E.802.1x authentication cannot be configured on a port configured for a voice vlan.
F.Port security cannot be configured on a port that is configured for a voice vlan.
Answer: B D
CDP (Cisco Discovery Protocol) must be enabled on switch port connected to IP Phone to recognize the IP Phone by switch and enable Port Fast to bring switch port directly from blocking to forwarding state. The Port Fast feature is automatically enabled when voice VLAN is configured. When you disable voice VLAN, the Port Fast feature is not automatically disabled.

Which three QoS mechanisms can be configured to improve VoIP quality on a converged network? Select three.
A. The use of a queuing method that will give VoIP traffic strict priority over other traffic
B. The use of RTP header compression for the VoIP traffic.
C. The proper classification and marking of the traffic as close to the source as possible
D. The use of 802.1QinQ trunking for VoIP traffic
E. The use of WRED for the VoIP traffic
Answer: ACE
In order to optimize the quality of VOIP calls, QoS should be implemented to ensure that VOIP traffic is prioritized over other traffic types.
By providing a strict queue for VOIP traffic, you will ensure that voice calls take precedence over the other traffic types.
In order to properly provide for QoS across the network, the voice traffic should be marked to give priority as close to the source as possible. This will ensure that the traffic is prioritized end to end.
Finally, WRED (Weighted Random Early Detection) could be configured to prevent congestion. WRED can be used to selectively drop less important traffic types, instead of dropping the voice packets when links become busy.
Incorrect Answers:
B: Compression can be used to lower the bandwidth required to transmit VOIP calls, but it will not help with improving the voice quality. In general, compression of any kindlowers the quality of VOIP.
D: The trunking method used will have no bearing on the VOIP quality.

This is a drag and drop question which is about the correct sequence of steps that a wireless client takes during the process of association with an access point (AP). Drag the items to the proper locations.



LDAP is being used throughout the Pass4sure wireless network. Which statement about the Lightweight Access Point Protocol (LWAPP) protocol is true?
A. The processing of 802.11 data and management protocols and access point capabilities is distributed between a lightweight access point and a centralized WLAN controller.
B. LWAPP advertises its WDS capability and participates in electing the best WDS device for the wireless LAN.
C. LWAPP aggregates radio management forward information and sends it to a wireless LAN solution engine.
D. LWAPP authenticates all access points in the subnet and establishes a secure communication channel with each of them.
Answer: A
The control traffic between the access point and the controller is encapsulated with the LWAPP.
The control traffic is encrypted via the Advanced Encryption Standard (AES). The data traffic between the access point and controller is also encapsulated with LWAPP. The data traffic is not encrypted. It is switched at the WLAN controller, where VLAN tagging and quality of service (QoS) are also applied.
The lightweight architecture splits the processing of the 802.11 protocol between two devices, the access point and a centralized Cisco WLC. The processing of the 802.11 data and management protocols and the access point functionality is also divided between the two devices. This approach is called split MAC.

You are a network administrator of a large investor relations company that uses a switched network to carry both data and IP telephony services. Why should you carry voice traffic on a separate VLAN?
A. IP phones require inline power and must be in separate VLAN to receive inline power.
B. IP telephony applications require prioritization over other traffic as they are more delay sensitive.
C. IP phones can only receive IP addresses through DHCP if they are in separate VLAN.
D.The CDP frames from the IP phone can only be recognized by the switch if the phone is in an auxiliary vlan.
Answer: B
Voice conversations don’t take up a lot of bandwidth, but the bandwidth they do is very delicate. If anything happens with the connection or the integrity of the data transfer in either direction the conversation won’t seam natural. To ensure the highest degree of integrity you should put voice traffic on its own separate VLAN and give that VLAN the highest priority.