Cisco 200-125 Exam

Which statement about QoS default behavior is true?

  • A. Ports are untrusted by default.
  • B. VoIP traffic is passed without being tagged.
  • C. Video traffic is passed with a well-known DSCP value of 46.
  • D. Packets are classified internally with an environment.
  • E. Packets that arrive with a tag are untagged at the edge of an administrative domain.
Answer: Option E.
Explanation: 

Frames received from users in the administratively-defined VLANs are classified or tagged for transmission to other devices. Based on rules that you define, a unique identifier (the tag) is inserted in each frame header before it is forwarded. The tag is examined and understood by each device before any broadcasts or transmissions to other switches, routers, or end stations. When the frame reaches the last switch or router, the tag is removed before the frame is sent to the target end station. VLANs that are assigned on trunk or access ports without identification or a tag are called native or untagged frames. For IEEE 802.1Q frames with tag information, the priority value from the header frame is used. For native frames, the default priority of the input port is used. Each port on the switch has a single receive queue buffer (the ingress port) for incoming traffic. When an untagged frame arrives, it is assigned the value of the port as its port default priority.
You assign this value by using the CLI or CMS. A tagged frame continues to use its assigned CoS value when it passes through the ingress port.

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