4A0-107 · Question #35
Click the exhibit button below. All interfaces are using their default trust states and MPLS is used as the transport tunnel. The SAP-ingress, SAP-egress, and network QoS policies have been…
The correct answer is D. The DSCP value will be set to af 12. E. Thedot1pvaluewillbesetto5. In a Nokia SR OS VPRN with MPLS transport, the SAP-ingress policy at PE1 classifies the incoming traffic using the dot1p value of 3 - not the DSCP BE - assigning it to a Forwarding Class (FC) and profile state. That FC and profile propagate across the MPLS tunnel via the…
Question
Click the exhibit button below. All interfaces are using their default trust states and MPLS is used as the transport tunnel. The SAP-ingress, SAP-egress, and network QoS policies have been configured as shown below. Assume that the default network-queue policy is used on each router. At router PE 1, customer traffic is arriving marked with DSCP BE and tagged with a dot1p value of 3. Based on the configuration shown below for the VPRN service, what will be the DSCP and dot1p marking for the packet egressing at router PE 2? (Choose two)
Exhibit
Options
- AThe DSCP value will be set to af21.
- BThe DSCP value will be set to be.
- CTheDSCPvaluewillbesettoaf23.
- DThe DSCP value will be set to af 12.
- EThedot1pvaluewillbesetto5.
- FThedot1pvaluewillbesetto2.
- GThe dot1p value will be set to 3.
How the community answered
(24 responses)- A17% (4)
- C4% (1)
- D58% (14)
- F13% (3)
- G8% (2)
Explanation
In a Nokia SR OS VPRN with MPLS transport, the SAP-ingress policy at PE1 classifies the incoming traffic using the dot1p value of 3 - not the DSCP BE - assigning it to a Forwarding Class (FC) and profile state. That FC and profile propagate across the MPLS tunnel via the network QoS policy, and at PE2 the SAP-egress policy re-marks the packet: in this configuration, the FC/profile combination maps to DSCP af12 (D) and dot1p 5 (E) on the customer-facing egress.
Why the distractors fail:
- B (DSCP BE) is wrong because DSCP is not preserved end-to-end in a VPRN - SAP-egress always re-marks based on FC/profile, overwriting the original DSCP.
- G (dot1p 3) is wrong for the same reason: the original dot1p is consumed for ingress classification and is not carried through to the egress re-marking.
- A (af21), C (af23), F (dot1p 2) represent mismatched FC or profile-state combinations that don't align with what the SAP-ingress policy derives from dot1p 3 in this specific configuration.
Memory tip - "Classify, Carry, Re-mark": At SAP-ingress the original markings are used up for classification; the FC+profile is what travels across MPLS; and the SAP-egress policy freshly stamps new DSCP and dot1p values. Never assume the customer's original markings survive to the far-end CE.
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