4A0-107 practice question 5 of 30

In a Nokia 7750 SR, which of the following QoS policies CANNOT include packet classification criteria?

Full set: 231 questions
Answer options
A: SAP-ingress
B: SAP-egress Correct answer
C: Network-queue
D: Network
Correct Answer:
B. SAP-egress
Explanation

In Nokia's Service Router Operating System (SR OS), Quality of Service (QoS) policies are specialized for different functions and application points. A SAP-egress policy is applied to traffic leaving a Service Access Point (SAP) towards the customer. Its primary function is to manage the scheduling and shaping of traffic that has already been classified into Forwarding Classes (FCs) by an ingress policy. The SAP-egress policy defines the egress queues, their parameters (e.g., CIR, PIR), and maps the pre-determined FCs to these queues. It does not contain any criteria for inspecting packet headers (L2/L3/L4) to perform classification; that function is handled at ingress.

Why Incorrect

A. SAP-ingress: This policy is fundamentally designed for packet classification. It uses criteria like IP/MAC addresses to classify traffic entering a SAP into different forwarding classes.
C. Network-queue: While this policy also lacks packet classification criteria, it is a template policy that only defines the parameters of network egress queues. It is not applied directly to an interface but is referenced by a network policy.
D. Network: A network policy can contain classification criteria. Specifically, on ingress, it classifies packets based on Layer 3 markings like DSCP or IP Precedence.

References

1. Nokia 7750 SR OS Quality of Service Guide, Release 21.10.R1, Section: "QoS Policy Entities".

Page 93, "SAP Ingress Policies": "Classification rules are configured in the SAP ingress QoS policy to select traffic for a specific forwarding class. The classification rules can be based on IP or MAC header fields..." This confirms that SAP-ingress policies include classification.

Page 100, "SAP Egress Policies": "A SAP egress policy is applied to a SAP to control the QoS of packets going out of the SAP. The policy defines the queues and the forwarding class-to-queue mappings." This section details queue management and FC mapping, with no mention of packet classification criteria.

Page 123, "Network Policies": "Network ingress traffic can be classified by matching the IP ToS/DSCP field or the MPLS EXP bits to a specific forwarding class." This confirms that network policies include classification.

Page 131, "Network Queue Policies": "Network queue policies define the network egress queues. The network-queue policy defines the forwarding class queue characteristics." This describes the policy as a template for queue definitions, distinct from a directly applied policy like SAP-egress.

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