Exam 400-101 topic 1 question 90 discussion

Actual exam question from Cisco's 400-101

Question #: 90
Topic #: 1

[All 400-101 Questions]

Which command enables L2 QoS support in all VLANs (including the native VLAN)?

A. switchport priority extend cos
B. mls qos trust dscp
C. mls qos rewrite ip dscp
D. switchport trunk native vlan tag

Show Suggested Answer

Suggested Answer: D 🗳️
You can enter the switchport trunk native vlan tag command to enable the tagging of native VLAN traffic on a per-port basis. When tagging is enabled, all the packets on the native VLAN are tagged and all incoming untagged data packets are dropped, but untagged control packets are accepted. When tagging is enabled, it will allow for L2 QoS support in all VLANs, including the native VLAN.

by maj at Dec. 15, 2019, 2:02 p.m.

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mmccabe

5 years, 5 months ago

Layer 2 802.1Q frame headers have a 2-byte Tag Control Information field that carries the CoS value in the three most-significant bits, which are called the User Priority bits. On interfaces configured as Layer 2 802.1Q trunks, all traffic is in 802.1Q frames except for traffic in the native VLAN. https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/25ewa/configuration/guide/conf/qos.html

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maj

5 years, 6 months ago

the correct answer is "mls qos trust dscp"

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