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352-001 · Question #271
352-001 Question #271: Real Exam Question with Answer & Explanation
The correct answer is C: Assign VLAN 100 to instance 1 and VLAN 200 to instance 2.. When VLAN trunking is prohibited and untagged interfaces are used, MST instance mapping must place each VLAN in a separate instance so distinct logical topologies can provide redundancy across the untagged links.
Question
Refer to the exhibit. You are designing a network using the Multiple Spanning Tree Protocol for loop avoidance. VLAN trunking is not allowed due to security requirements. Which option describes how you can design this Layer 2 network while using untagged interfaces between both switches?
Exhibit
Options
- AAssign VLAN 100 and VLAN 200 to the IST instance.
- BAssign VLAN 100 and VLAN 200 to instance 1.
- CAssign VLAN 100 to instance 1 and VLAN 200 to instance 2.
- DAssign VLAN 100 to the IST instance and VLAN 200 to instance 1.
Explanation
When VLAN trunking is prohibited and untagged interfaces are used, MST instance mapping must place each VLAN in a separate instance so distinct logical topologies can provide redundancy across the untagged links.
Common mistakes.
- A. Assigning both VLANs to the IST (Internal Spanning Tree) instance places them in the same topology, eliminating per-VLAN load balancing and defeating the purpose of MST instance separation.
- B. Placing both VLANs in instance 1 provides a single shared topology with no ability to use a second instance for a redundant or load-balanced path.
- D. Using the IST instance for production VLAN 100 is not recommended because the IST is reserved for MST internal communications and carries all VLANs not explicitly mapped to a named instance, which undermines deterministic design.
Concept tested. MST instance VLAN mapping with untagged interfaces
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