350-501 Architecture Practice Question
A service provider is building a new network slicing architecture to offer differentiated services to enterprise customers. The architecture uses SRv6 with network slices identified by slice IDs embedded in the SRv6 SID. The underlay is an IP network with ISIS. Each slice will have dedicated resources in the core, including guaranteed bandwidth and low latency. The plan is to use the SRv6 network programming concept to steer traffic into different slices. The provider wants to ensure that slice isolation is maintained end-to-end, including at the egress PE where traffic is handed off to the customer. However, during testing, they observe that traffic from one slice is incorrectly entering another slice's queue on an intermediate node, causing performance interference. The intermediate node is a transit router that does not terminate SRv6 but performs 'SID-based forwarding'. Which mechanism is most likely missing to ensure slice isolation on transit nodes?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The transit nodes are not configured to enforce per-slice QoS policies based on the slice ID in the SID.
Transit nodes must have per-slice QoS policies that map the slice ID (carried in the SID) to dedicated queue resources. Without such policies, all traffic may be mapped to a default queue, breaking isolation. The SID can indeed carry the slice ID; egress PE stripping or ingress PE misconfiguration would affect other nodes, not specifically transit.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The transit nodes are not configured to enforce per-slice QoS policies based on the slice ID in the SID.
Why this is correct
Correct. Transit nodes need to recognize the slice ID and apply appropriate queuing; otherwise, slices compete for resources.
- ✗
The SRv6 SID does not carry the slice ID; it only carries the locator.
Why it's wrong here
Incorrect. SRv6 SIDs can include a slice ID via arguments or flags.
- ✗
The egress PE is misconfigured to strip the slice ID before forwarding.
Why it's wrong here
Incorrect. Egress PE stripping would affect egress, not transit node behavior.
- ✗
The ingress PE is not setting the slice ID correctly.
Why it's wrong here
Incorrect. If slice ID were not set, all traffic would be unmarked, not just transit queue misplacement.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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