350-501 Question #193: Real Exam Question with Answer & Explanation

Question

A service provider is using QoS to manage customer traffic over the MPLS backbone. Which three statements about the behavior of each MPLS QoS mode based on QoS policy in the service provider core are true? (Choose three.)

Options

• AUniform mode does not change the original CE IP packet markings.
• BUniform mode changes the original CE IP packet markings.
• CPipe mode does not change the original CE IP packet markings.
• DPipe mode changes the original CE IP packet markings.
• EShort-pipe mode does not change the original CE IP packet markings.
• FShort-pipe mode changes the original CE IP packet markings.

Explanation

MPLS QoS modes dictate how IP QoS markings are handled within the MPLS domain and whether the original IP packet QoS markings are preserved or changed at the network edge.

Common mistakes.

• A. This statement is false because Uniform mode does change the original CE IP packet markings at egress if the EXP bits were modified.
• D. This statement is false because Pipe mode does not change the original CE IP packet markings; it preserves them.
• F. This statement is false because Short-pipe mode does not change the original CE IP packet markings; it preserves them.

Concept tested. MPLS QoS modes (Uniform, Pipe, Short-pipe)

Reference. https://www.cisco.com/c/en/us/td/docs/ios/mpls/configuration/guide/12_4t/mp_12_4t_book/mp_qos_imp.html

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