Which three descriptions are true? (Choose three.)

Question

Options

• AThe class of service is a parameter that is used for traffic classification and marking at Layer 2.
• BThe IP precedence is a parameter that is used for traffic classification and marking at Layer 2.
• CThe differentiated services code point is a parameter that is used for traffic classification and
• DThe class of service is a parameter that is used for traffic classification and marking at Layer 3.
• EThe IP precedence is a parameter that is used for traffic classification and marking at Layer 3.
• FThe differentiated services code point is a parameter that is used for traffic classification and

• A
  94% (44)
• B
  4% (2)
• D
  2% (1)

Explanation

QoS marking occurs at both Layer 2 and Layer 3, using different fields. A is true: Class of Service (CoS) is a Layer 2 marking mechanism that uses 3 bits in the 802.1Q VLAN tag header of Ethernet frames to classify traffic. B is false: IP Precedence is a Layer 3 mechanism, not Layer 2. C/F refer to DSCP (Differentiated Services Code Point), which uses 6 bits in the IP header's DSCP field - this is a Layer 3 marking mechanism, so F is true. D is false: CoS is Layer 2, not Layer 3. E is true: IP Precedence uses the first 3 bits of the IP header's Type of Service (ToS) byte, making it a Layer 3 classification and marking mechanism. In summary: CoS = Layer 2, IP Precedence = Layer 3, DSCP = Layer 3.

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