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350-801 · Question #574

Which QoS change occurs by default when traffic enters through an untrusted port?

The correct answer is B. remarking of the CoS field to 0 and the DSCP field randomly. When traffic enters a Cisco switch through an untrusted port, QoS policies automatically reset the CoS (Class of Service) field to 0 and may modify the DSCP (Differentiated Services Code Point) field based on the configured policies. By default, untrusted ports mark CoS as 0 to…

Infrastructure and Quality of Service

Question

Which QoS change occurs by default when traffic enters through an untrusted port?

Options

  • Aremarking of the CoS field to 1 and the DSCP field to 1
  • Bremarking of the CoS field to 0 and the DSCP field randomly
  • Cremarking of the CoS field to 16 and the DSCP field to 16
  • Dremarking of the CoS field to 46 and the DSCP field to 46

How the community answered

(68 responses)
  • A
    9% (6)
  • B
    87% (59)
  • C
    3% (2)
  • D
    1% (1)

Explanation

When traffic enters a Cisco switch through an untrusted port, QoS policies automatically reset the CoS (Class of Service) field to 0 and may modify the DSCP (Differentiated Services Code Point) field based on the configured policies. By default, untrusted ports mark CoS as 0 to ensure that untrusted devices (such as endpoints or unauthorized devices) cannot manipulate QoS settings. The DSCP field may be remarked depending on the QoS trust settings on the switch. Trusted ports (e.g., uplinks to other switches or trusted devices) allow CoS/DSCP values to pass through unchanged.

Topics

#QoS#CoS#DSCP#Trust Boundary

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